ML20195D561

Proceedings of Fhwa/Nceer Workshop on Natl Representation of Seismic Ground Motion for New & Existing Highway Facilities

ML20195D561
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Site:	Paducah Gaseous Diffusion Plant
Issue date:	09/22/1997
From:	Friedland I, Mayes R, Power M External (Affiliation Not Assigned)
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NCEER-97-0010, NCEER-97-10, NUDOCS 9811180097
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Proceedings of the FHWA/NCEER Workshop on the National Representation of Seismic Ground Motion for New and Existing Highway Facilities held at Park Plaza Hotel Butlingame, Califomia May 29-30.1997 Edited by I.M. Friedland'. M.S. Power and R.L. Mayes' 2

Publication Date: September 22,1997 Technical Report NCEER 97@l0 Organized by M.S. Power and R.L Mayes under NCEER Highway Project Task Number 106-F-5.4.1 and Applied Tec'hnolog CouncilProject ATC-18-1 FHWA ContractNumberDTFH61-92-C-00106 1 Assistant Director for Bridges and Highways, National Center for Earthquake Engineering Rescamh 2 Vice Pmsident. Geomatrix Consultants. Inc.

3 President, Dynamic Isolation Systems NATIONAL CENTER FOR EARTHQUAKE ENGINEERING RESEARCH State University of New York at Buffalo Red Jacket Q'W=nete, Buffalo, NY 14261 9811180097 901110

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i CHARACTERISTICS OF VERTICAL STRONG GROUND MOTIONS FOR APPLICATIONS

'IU ENGINEERING DESIGN Walter Silva, Pacific Engineering and Analysis 311 Pomona Avenue, El Cerrito, CA 94530 i

Introduction j

In the near-source region (D 5 10 to 15 km) of large canhquakes, the characteristics of strong ground motions change in stable and predictable ways: durations become significantly shorter (Chang et al. 1996; Abrahamson and Silva,1997), velocity and displacement time histories can increase significantly in amplitude and become more pulse like (depending upon rupture directtvity effects), long period fault normal motions show a stable increase over fault parallel motions (Somerville et al.,1997), and short period venical motions can exceed horizontal motions (Niazi and Bozorgnia,1991; Bozorgina et al.,1995) at both rock and soil sites (EPRI, 1993).

4 For vertical motions, these recent observations s' ggest that the commonly adopted venical-to-u horizontal response spectral ratio of 2/3 (Newmark and Hall,1978) may be signifleantly i

exceeded at short periods in the near-source distance range. With the increase in near-source strong motion recordings at both rock and soil sites to aid in constraining empirical attenuation relationships as well as providing direct estimation of statistical spectral shapes for vertical and horizontal components, it is possible to examine the We f the vertical-to-horizontal o

r-= spectral ratio (WH) on magnitude, distance, and site conditions.

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As an additional and important aspect, similarities and diffemnces in the characteristics of the i

time histories between vertical and horizontal motions can be eaamined. For design motions, i

the relative phasing t,ci. horizontal and vertical motions can be an important issue, leading to different structural analyses and design decisions depending on whether or not significant j

energy is expected to occur both venically and horizontally at or nearly the same time.

1 Effects of Site Conditions on the Characteristks of Vertical and Horizontal Strong Ground 3

l-Motions To I:stadly classify strong modon recordings sites into rock or soll, the Geomatrix categorization criterion listed in Table 1 is used. While the distinction between rock and soilis becoming less clear for Western United States (WUS) sites as more rock sites are drilled and velocities determined (EPRI,1993; BNL,1997), this largely qualitative classification scheme does capture 4

significant and stable differences in strong ground motions (Sadigh et al.,1997; Abrahamson and Silva,1997; BNL,1997).

Generic Rock and Soil Site Velocity Proflies To have an appreciations for the compression-and shear wave velocity proflies implied by the j

rock and soil categories (Table 1), Figures I and 2 show median (lognormal distribution) and 4

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l t 1 (r velocity profiles compuied for the two categories. The velocity profiles were computed from measured (downhole or crosshole) velocities at strong motion sites classified as Geomatrix A or B (Figure 1) or C or D (Figure 2). For the generic rock site, a strong velocity gradient l

is seen in the top 150 ft with low near-surface shear-and compression wave velocities:

approximately 800 ft/sec and 1,600 ft/sec respective!y. The shear wave velocity value of about 800 ft/sec departs significantly from the classically assumed value of about 2,503 ft/sec which is apparently not reached, on average, until a depth of about 70 to 100 ft. With such low near-i surface velocities, these rock sites may be expected to show some nonlinear effects under very l

high loading conditions (BNL,1997).

The absolute variability of both the shear-and compression wave velocities is high (COV 0.5 to 0.6) and there is little to suggest the presence of the water table at a compression wave velocity of about 5,000 ft/sec. Contrasting the rock site profiles in Figure I with those of the soil in Figure 2, significant differences are immediately apparent. Interestingly, over the top l

50 ft or so, the compression-wave velocities are very similar for both the rock and soil sites.

For the soil site, with the much lower shear-wave velocities, a significantly higher Poission's l

ratio is implied reflecting a larger Vp/Vs ratio for soil than for rock. Additionally for the soil site, the effect of the water table on the compression-wave velocity is apparent in the nearly I

constant velocity of the fluid phase at about 5,000 ft/see at depths from around 100 ft to 250 ft.

Beyond about 200 ft, the compression wave velocity of the skeleton material exceeds that of the fluid phase which is reflected in the velocity increase with depth.

The velocity variability at the soil site, although much less in absolute variation, is similar to that of the rock site in a relative sense (A = 0.4 to 0.5). 'This suggests that strong ground motions may be more variable at rock than at soil sites.

To contrast the dynamic material properties between rock and soil sites further, Figures 3 and 4 show Poisson's ratios computed from the compression-and shear wave velocity profiles. The higher variability in dynamic material properties for the rock verses the soil sites is reflected in the larger variation in Poisson's ratio for the rock site (Figure 3 verses Figure 4). The rock site has the lower overall Poisson's ratio which increases with depth to about 70 ft, remains nearly constant to a depth of about 200 ft, and then decreases to a value near 0.25 at a depth of 500 ft. Interestingly, Poisson's ratio for the soil site (Figure 4) shows a similar trend but shifted nearly a constant amount to a depth of about 350 ft. Beyond about 350 ft, Poisson's ratio for the soil site decreases less rapidly than for the rock site, remaining at a value of around 0.4 to a depth of 500 ft.

The dashed lines on Figures 3 and 4 represent smooth Poisson's ratio models and are shown in Figure 5 for the ;eneric rock and soil sites. The similar patterns and nearly constant shift to a depth of about 350 ft are quite apparent in the smooth models, t

The differences in Poisson's ratio as well as the overall velocities between the rock and soil sites may have important implications for the differences in vertical and horizontal motions. At rock sites, even though the shallow shear-wave velocities are low, the steep velocity gradient results in shear-wave velocities exceeding 2,000 to 3,000 ft/see at depths of 50 to 70 ft. As a result, l

for the same level of control (input motions), nonlinear effects are expected to be much less l

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pronounced than at a corresponding soil site and generally confined to the top 50 to 100 ft. The l

higher rock velocities and shallower potentially nonlinear zone will also tend to confine nonlinear effects to higher frequencies (BNL,1997). If vertical motions are more linear than horizontal, perhaps due to lower strains for inclined SV-waves and contributions of P-waves, the magnitude i

i dependence of the V/H ratio would be expected to be less at rock sites than at soil sites. As magnitude increases, the higher loading levels induce more nonlinearity in the horizontal motions at soil sites than the rock sites. The venical motions, remaining relatively linear, simply scale up and broaden in spectral content as magnitude increases. As a result, the magnitude scaling of the V/H ratios should be inversely proportional to the profile stiffness: significantly larger for soil than for rock conditions.

In addition to the effects of overall stiffness, the large jump in Poisson's ratio at the soil / rock interface (or steep gradient) at soil sites (Figure 5) will have an important impact on incoming wavefields. For a generic California deep crustal model, the average shear-and compression-wave velocities at the surface are about 3,500 to 4,500 ft/sec and 6,500 to 8,000 ft/sec (BNL, 1997). For a deep generic soil site, Figure 2 shows shear-and compression wave velocities at a depth of 500 ft of about 2,000 ft/sec and 6,500 ft/sec respectively. Transition to rock at this depth then would likely involve a very steep shear wave velocity gradient with a factor of 2 or more jump in velocity. For the compression-wave, the transition is much less pronounced, a factor of only 1.0 to 1.2 on average. This consequence of the drop in Poisson's ratio in transiting from soil to rock, being manifested in a large jump in shear-wave velocity, will tend to refract (bend) incident shear-waves much more severely than incident compression waves.

In passing through the rock / soil transition zone, the incident shear-waves will become much more vertical than the incident compression waves. For incident SV-waves, this will have the effect of converting venical motions to horizontal motions while the compression-waves largely remain inclined until depths of 100 to 200 ft where they are amplified and refracted (bent to a more vertical incidence) by the shallow compression-wave gradient (Figure 2).

Since canhquake sources emit much larger shear-wave amplitudes than compression-wave amplitudes, by the ratio of the source region velocities cubed ((Vp/Vs)3 = 5), incident inclined SV waves may be expected to dominate vertical motions at close distances. At large distances, the SV-wave is beyond its critical angle and does not propagate to the surface very effectively (Kawase and Aki,1990). At a source depth of 8 km and a average or generic California crustal model (Figure 31) the SV-wave critical angle for geometrical ray theory occurs at an epicentral

' istance of about 5 km for a point source. Crustal heterogeneity and source finiteness (vertical d

eatent) would tend to extend this distance somewhat. Also, geometrical ray theory is appropriate for high frequencies and low frequency energy would tend to be refracted less by the shallow velocity gradients, also resulting in extending the distance to the SV-wave critical angle.

However, even considering these effects, the SV-wave is not likely to dominate the venical component at distances exceeding 10 to 20 km.

At soil sites, due to the large change in shear-wave velocity at the base of the profile and the accompanying wave refraction, compression waves may be expected to dominate the vertical motions at near as well as far distances. Additionally, because of the large compression-wave velocity gradient from the surface to depths of about 100 to 200 ft, shon period compression-waves will be amplified which will result in large shon period venical motions.

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Short-Period Time Domain Characteristics of Vertical Motions To illustrate the effects of site conditions on acceleration time histories for vertical and horizontal components, a series of plots from the CDMG initial earthquake data reports are presented. These plots show all three components for each site in a convenient format for illustrative purposes.

To consider first close in rock sites, Figure 6 shows three component acceleration time histories l

at the Pacoima Dam (Downstream) and Corralitos sites for the 1994 M 6.7 Northridge and 1989 i

M 6.9 Loma Prieta earthquakes. Bc:h sites are within about an 8 km fault distanc a and both sets of records show very similar motions on the horizontal and vertical components. Structures founded on rock conditions at close distances may then be expected to experience simultaneous horizontal and vertical demands at similar levels and over a fairly broad period range.

For close-in soil sites, Figure 7 shows distinctly different features in the Sylmar County Hospital and Arleta records for the Northridge earthquake As for the rock sites, the soil sites are close-in recordings at fault distances of 6.1 km for Sylmar and 9.2 km for Arleta. Unlike the rock site recordings however, the soil site records show strong short period motion arriving significantly before the large !;orizontal motions. Structures founded on deep soil would then be expected to experience vertical and horizontal demands significantly different than on rock conditions. The vertical demands at close in soil sites would generally be characterized as out of phase with the dominant horizontal motions and of much higher frequencies. The largest short period motions on the vertical component may arrive before that of the horizontal and will be larger than the short period horizontal motions. During the passage of the dominant horizontal component motions, the vertical demands on a structure could be characterized as random high-frequency chatter which may exceed lg at short periods. This is markedly different than the vertical motions at close in rock sites, which tend to show strong low frequency coherence with the horizontal motions.

For the more distant sites, Figure 8 shows some interesting features across the Gilroy array for motions due to the 1989 Lama Prieta earthquake. Rock sites Gilroy 6 and 7, at fault distances of 19.9 and 24.2 km respectively, show features similar to those at the close-in soil site: carlier arriving and high-frequency vertical motions out-of-phase with the dominant horizontal motions.

At rock site Gilroy 1 however, at a fault distance of 11.2 km, the vertical motions display early arriving high frequency energy as well as low frequency energy coherent with the dominant horizontal motions. A possible explanation for this behavior is that this site, at a fault distance of about 11 km, is in the transition region from close-in to more distant rock site characteristics.

An interesting and apparent contradiction to the expected close-in rock site characteristics are the recordings at Pacolma Kagel Canyon for the Northridge earthquake (Figure 9). This rock site is at a fault distance of 8.2 km, about the same distance as the Pacoima Downstream site (Figure 6), but displays soil site characteristics on the vertical component: early arriving high frequency energy'and out-of-phase motions with the horizontal components. As part of a recent.

Caltrans/NSF/EPRI sponsored project to Resolve Site Response issues Associated with the Noithridge Earthquake (ROSRINE), this recording site, as well as many others, has recently been drilled and logged. Based on the shear-wave velocity logging, the site is misclassified.

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l With sheir wt.ve velocities ofjust under 2,000 ft/see from about 100 ft to the bottom of the hole at about 300 ft, the site is closer to a stiff soil than rock (Figures 1 and 2). This is not entirely unexpected being comprised of the Saugus formation, a typically soft Los Angeles area sandstone.

For the distant (D 2 10 to 15 km) soil sites, Figure 10 shows the remaining sites across the Gilroy array which recorded the Loma Prieta earthquake. Site Gilroy 2 is at fault distance ci 10.7 km and sites 3 and 4 are at fault distances of 14.4 and 16.1 km respectively. As with the close-in soil sites (Figure 7) and the distant rock sites (Figure 8), the vertical motions show high fregt;ency early arriving energy and little coherence with the dominant horizontal motions.

Hese acceleration time history plots are intended to illustrate general trends in short period vertical and horizontal motions. The intent is to show dominately SV motion, for close distances (s 10 to 15 km) on the vertical component with similar phasing as the horizontal components for rock sites while at soil sites, compression waves dominate the vertical motions showing earlier arriving and larger higher frequency energy content.

At more distant sites, compressional wave energy tends to be dominant on the vertical component at both rock and soil sites.

Response Spectral Characteristics of Vertical Motions To examine distance and site condition dependencies of vertical rnotions in more detail, as well as broader period range, Figures !I to 18 show 5% damped pseudo absolute response spectra as well as acceleration, velocity, and displacement time histories for a selected set of sites.

Cases examined are close-in and more distant rock and soil sites. Acceleration, velocity, and displacement time histories are plotted to show that at close-in soil sites and at more distant rock and soil sites, long period coherence exists between vertical and horizontal components. This results in the dominant long period motions being "in-phase" in the sense that the largest long period motions occur around nearly the same time on both the vertical and horizontal components.

For the close-in rock site, Figure 11 shows response spectra computed for the vertical and two horizontal component records at the Southern California Edison Lucerne site from the 1992 M 7.2 Landers canhquake. The fault distance is about 2 km and the vertical component slightly exceeds the horizontal components at periods shorter than about 0.1 sec. At long periods, beyond about I sec, the vertical is comparable to the smaller of the horizontal components, the fault-parallel motion. The period range of nearly constant spectral acceleration in the horizontal components, about 2 to 5 sec, is likely due to the effects of directivity.

The corresponding time histories are shown in Figure 12 and reveal strong coherence among components. The maximum velocity and displacement of the vertical component exceed those of the fault-parallel cornponent. 'Ite maximum venical displacement is about 15 cm or about 6 inches occurring over a 2 see period of time during which the fault-normal direction moved nearly 2 feet (= 60 cm).

For the close-in soil site, Figures 13 and 14 show the response spectra and time histories at the 5

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Arleta site for the 1994 Nonbridge earthquake. The fault distance is 9.2 km and the vertical component greatly exceeds the horizontal components at periods shorter than about 0.2 sec.

Beyond about 2 sec, as with the rock site Luceme, the vertical component becomes comparable to the horizontal. The time histories are shown in Figure 14 and indicate long period coherence i

and out-of phase short period energy (Figure 7).

For the more distant sites Figures 15 and 16 show response spectra and time histories for the l

Gilroy array no. 6 rock site and Figures 17 and 18 show corresponding plots for the Gilroy l

array no. 4 soil site. The carthquake is the 1989 Loma Prieta and the distances are 16.1 and 19.9 km for sites 4 and 6 respectively. For both sites, the short period vertical motions relative to the corresponding horizontal motions are significantly reduced compared to the close-in sites.

l Interestingly, as with the close-in sites, the long period vertical motions approach the horizontal l

motions for periods beyond about 2 to 4 sec. This feature is not predicted by either empirical or numerical modeling and suggests that venical motions are associated with high variability.

The corresponding time histories, Figures 16 and 18, show the usual partem; carly arriving short period energy on the verticals, out-of phase with the horizontal motions with longer period l

motions becoming more in phase between the components.

Magnitude Site, and Distance Dependencies of Hcrizontal and Vertical Component Response Spectral Shapes To examine empirically the role of possible site nonlineanty in the V/H ratios, statistical spectral shapes (Sa/PGA) were computed for magnitude bins centered on M 5.5 and M 6.5 for both rock and soil sites. The magnitude bins are one-half unit wide (M 5.5 = M 5 - 6, M 6.5 = M 6 -

l 7+) to include enough records to produce smooth and stable shapes.

The distance range was truncated at 50 km to avoid the effects of distance dependencies on the shapes. Records were selected from the PE&A strong motion database which includes available strong motion data for M ;t 4.5. For this application only canhquakes occurring in tectonically active regions were selected (the 1995 M 6.9 Kobe earthquake is included).

To examine the effects of the level of loading on the vertical and horizontal component spectral shapes, two distance bins were selected: 0 to 10 km and 10 to 50 km. For M 5.5 rock sites, Figure 19 shows the horizontal and vertical statistical shapes. To usess nonlinear effects, Figure 19 shows shapes computed for the two distance bins: 0 to 10 km and 10 to 50 km. The vertical spectral shapes (dashed lines) show more short period energy than the horizontal shapes (solid and dotted lines) and about the same level of maximum spectral amplification. The i

l vertical shapes have a maximum spectral amplification near 0.1 see whereas the shapes for the horizontal component peak near 0.2 sec. This difference is likely due to differences in damping with the vertical component showing significantly less damping than the horizontal. The lack of any significant distance dependency in this shift in peak spectral amplification between the vertical and horizontal components suggests that the differences in damping is occurring in the shallow portion of the path and that the sites are behaving in a linear manner as well. The shallow crustal damping is thought to occur in the top I to 2 km of the crust (Anderson and Hough 1984; Silva and Darragh,1995) and is generally modeled as a frequency independent i

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exponential damping term with a damping parameter termed kappa:

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(I) where H is the depth of the damping zone (1 to 2 km). 6 and 6 are the average shear-wave velocity and quality factor over the depth H and 5 is the corresponding damping ratio (decimal).

Response spectral shapes depend strongly on kappa, shifting to shoner periods u kappa decreases (Silva and Darragh,1995). To illustrate this effect, Figure 20 shows response spectral shapes computed using a simple point source model with kappa values ranging from 0.006 see to 0.160 sec. The shift in shape with kappa is easily seen and a peak near 0.2 see is consistent with a kappa value of about 0.04 see while a factor of two shift in the peak to about 0.1 sec corresponds to a similar shift in kappa value to about 0.02 sec. Interestingly, the factor of 2 shift in kappa for the verticals (x Kg/2) w4s also found by Anderson (1991) in a detailed v

analysis of vertical and horizontal motions recorded at rock sites. The kappa or shallow crustal damping effect is the likely mechanism controlling the large shift in spectral shapes between soft rock WUS spectral shapes and hard rock CEUS 'pectral shapes (Silva and Darragh,1995) and s

will impact hard rock venical spectral shapes as well as horizontal component shapes.

To continue the shape comparison for rock sites, Figure 21 shows horizontal and vertical shapes computed for M 6.5 (M 6.0 - 7+) at the two distan:e ranges: 0 to 10 km and 10 to 50 km. As with the M 5.5 shapes, there is a distinct shift in the peak amplification frequency between vertical and horizontal spectra of nearly 2. Also there does not appear to be a strong distance or loading level effect on either the vertical or horizontal shapes suggesting largely linear response at these ground motion levels.

To consider soil sites, Figures 22 and 23 show the vertical and horizontal response spectral shapes for M 5.5 (M 5.0 - 6.0) and M 6.5 (M 6.0 - 7+) earthquakes. As with the M 5.0 rock shapes, there is about a factor of two differen:e in the periods of maximum spectral amplification between the vertical (near 0.1 sec) and horizontal shapes (near 0.2 sec). Also there is no appreciable and stable shift in either the vertical or horizontal shapes with loading level (0 - 10 km or 10 - 50 km) reflecting largely linear response. Similar periods of peak amplification between rock and soil of about 0.2 see for the horizontal and 0.1 see for the vertical suggests similar low strain damping values at both rock and soil sites.

For the M 6.5 (M 6.0 - 7+) shapes, shown in Figure 23, the horizontal soil shapes show a well defined and broad-band shift between 10 to 50 km and 0 to 10 km. The horizontal shape for 10 to 50 km peaks near 0.2 see while that for 0 to 10 km peaks near 0.3 sec, crosses the 10 to 50 km shape, and maintains the shift from 0.1 see to nearly 10 sec. There characteristics are very similar to those shown in Figure 20 which illustrated the effects of kappa on response spectral shapes. These results suggest nonlinear response resulting in an overall increase in kappa from about 0.04 sec (linear soil response) to about 0.06 to 0.08 sec at the higher loading levels.

For the vertical component in Figure 23, a slight shift appears to be present between the shapes

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computed for the O to 10 km and 10 to 50 km bins but the shift is in the wrong direction and is not stable with period, crossing at about 0.1 and again near 2.0 sec. This is likely due to a sampling problem with too few sites contributing to the close-in (0 to 10 km) shapes.

The analyses of response spectral shapes revealed several features of interest: 1) a consistent shift in shapes between vertical and horizontal components at both rock and soil sites indicating lower shallow crustal damping for vertical components by about a factor of about 2,2) similar low-strain damping values for rock and soil sites, and 3) horizontal component soil shapes show nonlinear response characterized by a stable and broad band shift in shape to longer periods at higher loading levels. These features will be important factors in understanding the effects of magnitude, distance, and site condition on vertical to-horizontal response spectral ratios.

Empirical and Numerical Model Estimates of the Ver11 cal-to-Horizontal Response Spectral Ratios To provide estimates of vertical-to horizontal ratios as functions of magnitude, distance, and site conditions, a combination of empirical attenuation, relations and numerical modeling is used.

While the empirical relations are reasonably well constrained for WUS (or tectonically active regions), little data exist for M greater than 5.0 for CEUS conditions at distances ofinterest (D s 20 km).

The only large magnitude earthquake considered representative of the CEUS and which generated close in strong motion records is the M 6.8 1985 Nahanni earthquake. It was recorded at only three sites, all hard rock, and all within 20 km of the source. This earthquake, along with smaller magnitude CEUS hard rock recordir gs, clearly show significantly different spectral content between WUS and CEUS horizontal rock motions. This feature is illustrated in Figure 24 which contrasts WUS and CEUS horizontal component rock site response spectral shapes for M around 6.5 and 4.0. The difference in short period spectral content between WUS and CEUS is significant and consistent between different magnitude earthquakes and is attributed to differences in shallow crustal damping or kappa values (Silva and Darragh,1995). For CEUS rock site vertical components, an open question exists as to whether they show a shift to even shorter periods than the horizontal components (see Figure 21 for WUS rock). The effective bandwidth of current recordings is not capable of resolving this issue, however if similar physical mechanisms are controlling the motions at WUS and CEUS rock sites, some degree of shift would be expected and should be reflected in estimates of CEUS V/H ground motion ratios.

These differences in rock site spectral content may also have implications to soil motions since WUS and CEUS control motions, as well as rock outcrop motions, would be expected to have differences in spectral content. The differences in WUS and CEUS control motion spectral content may not result in significantly different deep soil horizontal motions due to the effects of material damping and nonlinearity. However, vertical component soil motions, if response I

remains largely linear in compression (constrained modulus), may have very high short period levels at close distances to large magnitude earthquakes (EPRI,1993).

Applications to WUS Rock and Deep Soil Siles v

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For rock sites, the ratios reflect the average of Sadigh et al. (1997) and Abrahamson and Silva j.

(1997) empirical relations, while for soil, because Sadigh et al. (1997) do not present a relationship for the vertical component, only Abrahamson and Silva (1997) relation is used.

I Figure 25 shows the empirical vertical and horizontal spectra (5% damping) for M 6.5 at a distance of 5 km for both rock and soil site conditions. The shifting of the peak response of the vertical spectra to shorter periods than the horizontal is present showing a crossing in spectral l

levels at short periods. At this close distance (D = 5 km), response spectral ratios (V/H) would -

j then exceed I at short periods and drop significantly at longer periods.

. To look at the distance dependency of the V/H ratio for WUS, Figure 26 shows empirical ratios computed for both rock and soil sites. As expected, from the earlier examination of response j

spectra at individual sites (Figures 11,13,15, and 17), the rnaximum rock site V/H ratios are i

lower than the corresponding ratios for soil sites. For the rock sites, the distance dependency is considerably less than that for soil, a maximum of about 1.5 in going from 1 to 40 km. The larger distance dependence in the VIH ratios for soil sites may be due to nonlinear response of the soils: as distance increases reJatively less damping is occurring in the soll column.

To look at the magnitude dependency of the empirical V/H ratios, Figure 27 shows ratios for rock and soll sites computed for distances of I and 20 km. The magnitude dependence of the V/H ratios is stronger for soil sites than for ro::k sites, again possibly reflecting effects of j

nonlinearity. Additionally, the magnitude dependence decreases with increasing distance for both rock and soil sites. For rock sites, this may be an artifact of the magnitude saturation built imo the empirical relations, being different for rock and soil sites.

These empirical VIH ratios are reasonably well constrained and can provide the basis for developing smooth design ratios for WUS rock and deep moderately stiff soils. For applications to design motions, strong consideration should be given to adequate conservatism which should reflect the higher uncertainty in vertical motions compared to horizontal motions, particularly for close distances to large magnitude (M 2 7) earthquakes.

Applications to CEUS Rock and Deep Soil Sites Based on the comparisons of the spectral content between WUS and CEUS rock site spectral shapes shown in Figure 24, differences in rock, and possibly soil VIH ratios may be expected l

to occur between the two tectonic regions (EPRI,1993).

As previously discussed, due to the paucity of recordings (M 2 5, D st 50 km) reflecting CEUS conditions, some form of rnodeling is necessary to assess the appropriateness of WUS V/H ratios for engineering design applications.

Computational Model To model vertical motions, incident inclined compression waves from the stochastic point-source ground motion model (EPR),1993) are assumed incident at the top of the source layer and the P SV propagators of Silva (1976) are used to model the crust and soil response to inclined P-SV wavefields. The angle ofincidence at the top of the source layer is computed by two-point ray

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j tracing through the crust and soil column (if present) assuming incident compression-waves.

l To model soil response, a soil column is placed on top of the crustal structure and the incident j

inclined P-SV wavefield is propagated to the surface where the vertical (or radial) motions are l

computed.

l Treatment of Soil Response for Vedical Motions l

l Commonly, equivalent-linear site response analyses for venical modons have used strain iterated l

shear moduli from a horizontal motion analysis to adjust the compression-wave velocities assuming either a strain independent Poisson's ratio or bulk modulus. Some fraction (generally 100% to 30%) of the strain iterated shear wave damping is used to model the compression-wave damping and a linear analyses is performed for venically propagating compression waves using i

the horizontal control motions scaled by some factor near 2/3.

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The equivalent linear approach implicity assumes some coupling between horizontal and vertical motions. This is necessitated by the lack of well determined M/M,,, and damping curves for the constrained modulus. Ideally, the strain dependency of the constrained modulus should be l

determined independently of the shear modulus. Also, the conventional approach assumes l

vertically-propagating compression waves and not inclined P-SV waves. Additionally, the use l

of some fraction of the horizontal control motion is an approximation and does not reflect the j

l generally greater high frequency content of vertical component motions at rock sites due to lower l

kappa values (EPRI,1993).

l Alteratively, fully nonlinear analyses can be made using two-or three-component control l

motions (Costantino, 1967; 1969; Li et al.,1992; EPRI,1993). Thes: nonlinear analyses l

require two-or three dimensional soil models which describe plastic flow and yielding and the accompanying volume changes as well as coupling between vertical and horizontal motions through Poisson's effect. While these analyses are important to examine expected dependencies

.of comp

• ted motions on material properties and may have applications to the study of soil compaction, deformation, slope stability, and component coupling, the models are very l

sophisticated and require specification of many parameters, at least some of which are poorly I

understood.

In the cunent implementation of the equivalent linear approach to estimate vertical to horizontal response spectral ratios, the horizontal component analyses are performed for vertically propagating shear waves using an equivalent linear random vibration theory (RVT) methodology coupled to the point-source stochastic ground motion model (EPRI,1993; Schneider et al.,

1993). To compute the venical motions, a linear analysis is performed for incident inclined P-SV waves using low-strain, compression and shear wave velocities derived from the generic shear-and compression-wave velocity profiles (Figures ! and 2). Compression-wave damping is assumed to be equal to the low strain shear wave damping Dohnson and Silva,1981). The horizontal component and vertical component analyses are assumed to be independent.

l These approximations, linear analysis for the vertical component and uncoupled vertical and l

horizontal components, have been checked by comparing results of fully nonlinear analyses at t

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soil sites Gilroy 2 and Treasure Island to recorded venical and horizontal motions from the 1989 i

Loma Prieta canhquake (EPRI,1993). The nonlinear analyses indicate that little coupling exists between the vertical and horizontal motions for the ranges in control motions analyzed (maximum about 0.5g). These assumptions are expected to result in conservative estimates of vertical motions since a higher degree of coupling implies degradation of constrained modulus and an accomptnying increase in compression wave damping.

The point-source computational model has been validated for horizontal motions with the Loma

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Prieta earthquake by comparing recorded motions with model predictions (Schneider et al.,

1995) and more recently with 14 additional earthquakes (M 5.0 7.4) at about 500 sites. For vertical motions, current validation includes comparisons of recorded motions to model predictions for the 1989 M 6.9 Loma Prieta earthquake (20 rock and 16 soil sites),1992 M 7.2 l

Landers carthquake (3 rock and 9 soil sites), and the 1994 M 6.7 Northridge earthquake (16 l

rock and 56 soil sites). In general, vertical motions are not modeled as well as horizontal motions as the observed vertical motions show more variation than the horizontal and the model is not able to capture the increased variability. This is reflected in empirical relations as well, with a larger standard error associated with vertical motions (Abrahamson and Silva,1997).

As an example of model predictions to recorded' motions. Figure 28 shows recorded and computed vertical and horizontal motions for the M 7.2 Landers earthquake at the rock site Lucerne (D = 2 km). The simple point source, using the generic shallow rock profile with

- equivalent-linear analyses for the horizontal component and a linear analysis for the vertical appears to capture the general features of the recorded motions.

To generate V/H ratios based on numerical modeling, the shallow generic profiles (Figures 1 and 2) were placed on top of the generic California crust (Figure 31). For equivalent-linear analyses, recently developed rock and cohesionless soil gig,,,,, and hysteretic damping curves (BNL,1997) were used. The point-source stress drop was 60 bars, based on inversions of the Abrahamson and Silva (1997) empirical attenuation (BNL,1997), and the source depth is taken as 8 km (the same as in the inversions).

To compare simulated V/H ratios to the empirical, Figures 29 and 30 show results for rock and soil sites for M 6.5, the best constrained magnitude for the empirical relations. In general the 3

i model captures the overall shapes and trends, with distance of the empirical ratios but shows a much stronger close in distance effect. This strong distance effect is controlled by the incidence angle (top of source layer) increasing rapidly with increasing epicentral distance. As previously mentioned, crustal heterogeneity as well as source finiteness would tend to weaken this distance dependence. For the point source model, crustal randomization to simulate uncertainty and randomness in the crustal structure would reduce the near-source distance dependency making it similar to the empirical. However, the simple point source model, as implemented here, captures the general trends of the WUS empirical rock and soil V/H ratios well enough to provide guidance in assessing the appropriateness of applying WUS ratios to CEUS conditions.

To generate VIH ratios for the CEUS, a generic midcontinent crustal model is used (EPRI, l

1993). The CEUS crustal model is considered appropriate for hard rock sites in the CEUS cast l

of the Rocky Mountains with the possible exception of the Gulf Coast region. This region has

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i

a crustal structure somewhat intermediate between the WUS and the CEUS (EPRI,1993). The large difference between the two generic crustal models shown in Figure 31 gives rise to significantly different shon period strong ground motion characteristics at close-in distances (as depicted in Figure 24) as well as different rates of attenur. tion with distance. These differences may be expected to impact the V/H ratios as well. For the WUS ratios, both the empirical and numerical model results showed that the stiffer profile (rock verses soil) resulted in lower short period ( $ 0.3 sec) V/H ratios but larger long period ratios. For the hard rock CEUS crust, this trend may be expected to continue resulting in a lower maximum VIH ratio with perhaps a higher long period level. Due to the lower horizontal and vertical kappa values for the CEUS crust, the peak in the V/H ratio may be expected to occur at much shorter periods than in the l

CEUS rock ratios. These expected trends are reflected in the model prediction shown in Figure l

32 (top plot). For CEUS hard rock sites, the peak V/H ratio is significantly lower and at a shoner period than soft rock sites and the long period level is higher as well. This difference between WUS and CEUS in the period range of 0.1 to 1.0 see was also found by Atkinson and Boore (1997) in an empirical analysis of the H/V ratio of Fourier amplitude spectra at large distances (D 2 20 km) in Western and Eastern Canada.

For deep soil sites, Figure 32 (bottom) plot) su'ggests'that the V/H ratio may be significantly higher in the CEUS than in WUS. This result is primarily due to nonlinear soil response in the horizontal component as well as assuming linent response for the venicals. The factors i

contributing to the higher degree of nonlinear response for the CEUS soil ratios are the higher levels of high frequency energy in the control motions (Figure 24), the larger overall motions l

due to the higher stress drop (100 bars for CEUS and 60 bars for WUS), and the large jump in f

shear wave velocity in going from the base of the soil to the top layer of the CEUS crust (Figure 31). These results suggest that for both rock and soil CEUS VIH ratios, it is probably l

inappropriate to adopt WUS ratios for design purposes. A similar conclusion was reached in l

the EPRI (1993) project to estimate strong ground motion in the CEUS. In that project, design V/H ratios were developed for CEUS rock and stiff soil conditions based primarily on model simulations.

It should be emphasized that only a single and very simple model, which involves many assumptions, has been implemented here.

However, the results may provide a useful i

L contribution to developing design V/H ratios for CEUS conditions. Naturally, the most satisfying approach is to make use of multiple well validated models to assess the range in l

uncenainty in the CEUS V/H ratios.

L Conclusions l

Characteristics of venical and horizontal component strong ground motioM have been examined l

to reveal general trends which may be of significance to structural analyses. Recordings at both rock and deep soil sites representative of WUS showed distinctly different behavior of vertical motions at rock and soil sites at close source distances (D s 10 to 15 km). At rock sites, the l

largest motions tend to occur on all three components at nearly the same time and "in-phase

• motion is present on acceleration, velocity, and displacement time histories. Vertical component response spectra can exceed those of the horizontal components at shon periods (T s 0.1 sec) i by moderate amounts (20% on average) and at very close fault distances (D s 5 km).

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At soil sites, short period (T s 0.2 see) venical motions, as revealed by acceleration time histories, occur "out-of-phase

• with the largest motions on the horizontal components. For intermediate to-long periods, however, near-source soil site velocity and displacement time l

histories are "in phase", showing the dominant motion occurring at about the same time. At close source distances (D s 5 km) short period (T $ 0.1 see) vertical motions may exceed horizontal motions by a factor of 2.

Analyses of venical and horizontal component statistical response spectral shapes for both rock and soil sites at varying magnitudes and distances showed significantlyless damping at both rock and soil sites for vertical motions. These analyses also suggested that venical motions are largely linear at both rock and soil sites. Horizontal motions, on the other hand, for earthquakes of M 6.0 to 7.0+ and at source distances within 10 km showed a broad-band shift in spectral shape to longer periods consistent with an increase in damping accompanying nonlinear site response.

Response spectral ratios (V/H) were computed from median WUS empirical horizontal and vertical component response spectra at rock and soil sites for a suite of distances (Figure 26).

These empirical VIH ratios may be used to obtain rn,tios for applications to structural design for WUS conditions.

Nonlinear response in horizontal motions coupled with largely linear response for vertical motions at soil sites is expected to result in larger V/H ratios for soil sites compared to rock sites at close distances as well as a stronger magnitude dependency. This trend is seen in VIH ratios computed using empirical attenuation relations and at least a portion of these dependencies is attributed to nonlinear response involving horizontal motions at soil sites.

To estimate V/H ratios for CEUS hard rock and deep soil conditions, a simple point source l

model is used to predict both rock and soil horizontal and vertical motions. The model treats vertical motions as inclined P SV waves with a linear analysis and horizontal motions as vertically incident shear waves using equivalent linear analyses. Model predictions for WUS V/H ratios showed generally favorable agreement with empirical V/H ratios. Application of the

)

simple model to CEUS showed generally higher V/H ratios for hard rock sites compared to soft rock sites at long periods (T > 0.3 sec). At short periods, the peak in the V/H ratio is shifted from about 0.07 sec for soft rock to about 0.013 sec for hard rock. These results are due to the lower shallow crustal damping at the hard rock site.

For soil sites, the CEUS VIH ratio is predicted to be significantly larger than the conspwding WUS ratio. This is attributed to higher levels of nonlinear soil response on the horizontal motions due to CEUS rock control motions richer in short period energy, higher overall levels of control motions due to higher CEUS stress drops (100 bars compared to 60 bars), and a larger impedance contrast at the base of the soil column. Due to the simplicity of the model and the number of significant assumptions, use of multiple well validated models is recommended in developing design V/H ratios for the CEUS.

In general, the conventional V/H factor of 2/3 is probably not appropriate at CEUS rock and soil sites and may only be appropriate for WUS sites at periods beyond about 0.3 sec and for weWaswe.rpt315M 13

distances beyond about 50 km.

REFERENCES Abrahamson, N.A. and Silva, W.J. (1997). "Empin;al response spectral attenuation relations for shallow crustal canhquakes." Seism. Soc. Am.. 68(1),94-127.

Anderson, J.G. (1991). "A preliminary descriptive model for the distance dependence of the -

spectral decay parameter in southern California." Bull. Selsm. Soc. Am., 81(6), 2186-l 2193.

Anderson, J. G. and S. E. Hough (1984). "A Model for the Shape of the Fourier Amplitude i

Spectrum of Acceleration at High Frequencies." Bull. Seism. Soc. Am., 74(5),

1969-1993.

Atkinson, G.M. and Boore, D.M. (1997). "Some comparisons between recent ground motion relations." Seism. Res. Lett. 68(1), 24-40.

Bozorgina. Y., M. Niazi, and K.W. Campbell (1995). " Characteristics of free-field venical j

ground motion during the Northridge earthquake." Earthquake Spectra, !!(4),515-525.

i Bozorgina Y. and M. Niazi (1993). " Distance scaling of venical and horizontal response spectra of the Loma Prieta earthquake." Earthquake Engineering and Soil Dynamics. 22, 695-707.

Brookhaven National Laboratory (1997). " Description and validation of the stochastic ground motion model." Submitted to Brookhaven National Laboratory, Associated Universities, Inc. Upton, New York.

Chang, S.W., J.D. Bray and R.B. Seed (1996). " Engineering implications of ground motions from the Nonhridge canhquake." Bull. Seism. Soc. Am., 86(IB), S270-S288.

Electric Power Research Institute (1993). " Guidelines for determining design tsasis ground motions." Palo Alto, Calif: Electric Power Research Institute, vol.1-5, EPRI TR-102293.

Niazi, M. and Y. Bozorgnia (1991). " Behavior of near-source peak horizontal and vertical l

ground motions over sman 1, array, Taiwan." Bull. Seism. Soc. Am., 81(3), 715-732.

Newmark, N.M. and W.J. Hall (1978). " Development of criteria for seismic review of selected l'

nuclear power plants." NUREGICR-0098, Nuclear Regulatory Commission.

i l

Kawase H. and K. Aki (1990). " Topography effect at the critical SV-wave incidence: possible j

explanation of damage pattern by the Whittier Narrows. California, canhquake of 1 October 1987." Bull. Seism. Soc. Am., 80(1), 1-30.

..w

,..mm 14 i

I l

L L

Sadigh, C.-Y Chang, J.A. Egan. F. Makdisi, and R.R. Youngs (1997). " Attenuation relationships for shallow crustal earthquakes based on California strong motion data."

Sc/sm. Soc. A m., 68(1), 180 189.

1 Schneider, J.F., W.J. Silva, and C.L. Stark (1993). " Ground motion model for the 1989 M 6.9 Loma Prieta earthquake incl ding effects of source, path and site." Eanhquake Spectra.

9(2), 251-287.

Silva, W.J. and R. Danagh (1995). " Engineering characterization of earthquake strong ground motion recorded at rock sites." Palo Alto, Calif: Electric Power Research Institute, TR-102261.

Silva, W.J. (1976). " Body Waves in a Layered Anelastic soilid." Bull. Sels. Soc. Am.,66(5),

1539-1554.

Wald, D.J., Heaton, T.H. (1994). " Spatial and temporal distribution of slip for the 1992 Imders, California, earthquake." Bull. Scism. Soc. Amer., 84(3), 668-691.

I

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I Table 1 GCOMATRIX CONSULTANTS STRONG MOTION RECORDING STATIONS CLASSIFICATION SYSTEM Geotechnical Subsurface Characteristics Desienation Descriotion

'A Rock.

Instrument is founded on rock material (V, > 600 mps (1969 ft/sec) or a very thin veneer (less than 5m (16 ft)) of soil overlying rock material.

B

. Shallow (stiff) soil.

Instrument is founded in/on a soil profile up to 20m (66 ft) thick overlying rock material, typically in a narrow canyon, near a valley edge, or on a hillside.

C Deep narrow soil.

Instrument is founded in/on a soil profile at least 20m (66 ft) thick overlying rock material in a narrow canyon or valley no more than r,everal kilometers wide.

D Deep broad soil.

Instrument is founded in/on a soil profile at least 20m (66 ft) thick overlying rock material in a broad canyon or valley.

E Soft deep soil.-

Instrument is founded in/on a deep soil profile that exhibits low average shear-wave velocity (V < 150 mps (492 ft/sec)).

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GEOMATRIX CONSULTANTS STONG-MOTION RECORDING STATIONS 4

CLASSIFICATION SYSTEM Geotechnical Subsurface Characteristics Desienation Descriorion 4

A Rock.

i Instrument is founded on rock material (V3> 600 mps (1%9 ft/sec) or a very thin veneer (less than 5m (16 ft)) of soil overlying rock material.

B Shallow (stiff) soil.

Instrument is founded in/on a soil profile up to 20m (66 ft) thick overlying rock material, typically in a narrow canyon, near a valley edge, or on a hillside.

C Deep narrow soil.

Instrument is founded in/on a soil profile at least 20m (66 ft) thick overlying rock material in a narrow canyon or valley no more than several kilometers wide.

D Deep broad soil.

4 Instrument is founded in/on a soil profile at least 20m (66 ft) thick overlying rock material in a broad canyon or valley.

E Soft deep soil.

Instrument is founded in/on a deep soil profile that exhibits low average shear-wave velocity (V < 150 mps (492 ft/sec)).

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GE0 MATRIX SITE CLASS A & B Figure L. Median and i 1 a compression-and shear wave velocity profiles for Geomatrix site class A plus B (soft rock, Table 1).

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GE0 MATRIX SITE CLASS C & D Figure 2. Median and i 1 a compression-and shear-wave velocity profiles for Geomatrix site class C plus D (deep soil, Table 1).

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soil, Table 1).

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Mgave 6. Horizontal and vertical cc- ; - ^ acceleration tisme histories seconied at rock sites Pacoisa Downstream for the 1994 M 6.7 l

Northridge carthquake (top) and Corralitos for the 1989 M 6.9 lana Pneta carthquake (bottom). (Source: CDMG initial data reports).

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Mgure 7. Horizontal and vertical component acceleration time histories recorded at soil sites Sylmar (top) and Arleta (bottom) for the l

1994 M 6.7 Northridge earthquake. (Source CDMG initiai data reports).

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histories recorded at i

rock sites Gilroy 6. ~1, and i Gop, noiddle. and so-

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I Figure 9. Horizontal and vertical component acceleration time histories recorded at " rock" site Pacoima Kaget for the 1994 M 6.7 N G -ide, earthquee (Source: CDMG initial data reports).

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LANDERS 06/28/92 1158 LUCERNE LEGDQ 5

I R & PEnn-CORRECTED DATA, CO @ LP 5

IWAN & PE&n-CORRECTED DATA, CO@ 260 5

IWAN & PE&A-CORRECTED DATA, Com 345

-+-

Figure 11. 5% Damped pseudo absolute response spectra at the SCE rock site Luceme for the 1992 M 7.2 Landers earthquake. Fault distance is about 2 km,

l-o i

.a E:

.,% g

!',J V A,4.{'s, L

t

~u en

, ].

\\

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= : =: =-:'.'

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)

E :

', \\

.~

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g

's -

S

'?

2

,,,.h.

10 ~2 10 ~3 10 0 10 1 Period (seconds)

NORTHRIDGE 01/17/94 1231 ARLETA - NORDH0FF FIRE STA LEGEND 5

CDT. & PEM-CORRECTED DATA, CorV' LP 5

CD1C & PE15KORRECTED DATA, Cart' 090 5

CDr1C & PE&A-CORRECTED DATA, Coff 360 l

Hgure 13. 5% Damped pseudo absolute response spectra at the soil site Arleta for the 1994 M 6.7 Northridge earthquake. Fault distance is about 9 km.

e

-.v -

eo a

,f

{@ h'$ I?lh4

~

89 a

_g

- - ~//^j e

4 89 j

_g g

Eci

_ n, 1

2

-a gn Ed

-n

-i f

g bd

-n

-i&.

0 2

mo 3

.o 37 8

_5 3 8,

-N I

5 asa

.8

~. _

g a9 a.

a.

4.

s.

e.

to.

12.

LA.

ts.

te.

20.

TIME (SEC) l NORTHRIDGE 01/17/c)4 1231, ARLETA - NORDHOFF FIRE STA Figure 14. Acceleration, velocity, and displacement time histories at the soil site Arleta for the 1994 M 6.7 Northridge earthquake. Fault distance is about 9 km.

l

l Q

=.

C j

/\\

..( / \\

,,e j 7 /... q st$

/

V.,,5. C

~

• s (D

s\\

.8 e,

, \\,.,

.. \\'.

u e :

M

.\\

3, N

i,

\\\\-,,

,' c.

R 10 -2 to ~1 10 0 to 1 Period (seconds)

LOMA PRIETA 10/18/89 0004 GILROY ARRAY #6 LEGEND 5

PELA-CORRECTED DATA, Coff LP 5

PELA-CORRECTED DATA, Carp 000 5

PELA-CORRECTED DATA, CorF 090 j

i Figum 15. 5% Damped pseudo absolute response spectra at the rock site Gilroy 6 for the 1989 M 6.9 Loma Prieta earthquake. Fault distance is about 19 km.

L l

t

N

• -N Q;

^:.

30i N

_g

- - g1AL 89 N

o oso

^^"!%

• N l

a9

-n 1

_i

-n W-up bd

^

-n

.=

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090 k

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f i

O

_. -m g(

E i f g

i, c.

z.

4 s.

s.

io.

12.

14 is.

te.

20.

TIME (SEC)

LOMA PRIETA 10/18/89 0004, GILR0Y ARRAY 66 Figure 16. Acceleration, velocity, and displacement time histories at the rock site Gilroy 6 for the 1989 M 6.9 Loma Prieta earthquake. Fault distance is about 19 km.

i l

e l

I i

.. ii..

l g

1 o

'/,

=

o n

,,, ' ~, ', '

l v ', \\

j d

' \\,,3 g,

i,,

n/

., w<,,-

\\

J

~

s e

vs

/

1 l

\\

i E :

\\,' 'i l\\ '.

s i

t.

N, i.

i

?

(

,w.,

l R

10 ~2 10 ~I 10 0 10 I Period (seconds)

LOM9_PRIETA 10/18/89 0004 GILROY ARRAY #ed LEGND 5

PEM-CORRECTED DATA, Cor1P LP 5

PEM-CORRECTED DQTA, Corf 000 5

PCM-CORRECTED DATA, Corp 090 l

l Figure 17. 5% Damped pseudo absolute response spectra at the soil site Gilroy 4 for the 1989 M 6.9 Loma Prieta earthquake. Fault distance is about 16 km.

1 M

i o

ooo

.n Ua o' n

_g

~

-- : = i 9 2,L',y p + s _ -

~ - -

^

n eo e

n j

,f

~"n

~

eo

-Q

• _y

'E.

-o tw w

^

\\

$d 2

-o oso 3

3 ?,

N

\\

2~

000

\\l 5 {7 l

_a 5

g a7

_m 5.

A-J N

m 3y O.

2.

4.

G.

9.

10.

12.

14.

16.

19, 20.

T]ME (SEC)

LOMA PRIETA 10/18/89 0004, GILROY ARRAY $4 Figust 18. Acceleration, velocity, and displacement time histories at the soil site Gilroy 4 for the 1989 M 6.9 Loma Prieta earthquake. Fault distance is about 16 km.

i il o_

1 i.~>.: * ~ ',. ~

7

\\.,.

i

-r '*/..

s

\\

o

,,=

\\

s.

l s

s,.

s i

%,v*

,N

{

g 1

a u

5 T

L S i 0,.

i 5,,

y s

~

l

~,

R

• • J 10 -2 to -3 10 0 o.

Per iod (seconds )

MEDIAN SPECTRAL 5HAPES M 5.5 (5.D-6.0), ROCK LEEND HORIZONTAL M*5.51 (5.0-6.01, D 7.84 210-10 21, AVG PGA a 0,179 C, Z8 REC.

HORIZONTAL, Ms5.59 (5.0-6.01, D:21.70 M (10-50 21, RVG PGA s 0.10B G,192 REC.

VERTICnL, M 5.51 15.0-6.0), D 7.84 M (0-10 m ), AVG PGA s 0.124 C, 13 REC.

VERTICAL, M:5.5915.0-6.01, D=21.70 KM i10-50 mi, AVC PGA 0.067 C, BB REC.

i t

l Figure 19. Median statistical response spectral shapes (5% damping) computed from WUS data recorded at rock sites in the magnitude range of M 5 to M 6. Rupture distances range from 0 to 10 km and 10 to 50 km.

o

a K

0.%0 EC a

R N

_m K: 0.006 SCC

~

e tn 7

~

3 LEGEND 5

K s 0.006 EC 5 %,

K : 0.0t2 EC 5

K 0.024 EC

~

~

5 %,

K s 0.040 EC 5

K = 0.000 EC 5 %,

K : 0.%0 SEC 7

R 10 -2 3o -1 3a 0 10 %

Per iod (seconds )

Figure 20. He effects of kappa on 5% damped response spectral shapes computed for a M 6.5 ennhquake at 10 km using WNA parameters. As kappa increases, the peak shifts to longer periods and remains essentially constant in amplitude.

l l

g t

~

>4 /

'-s:..

/

f s,, % '.,

o Ns s,-

e ss m

3

\\ %'.

\\ s',

N y

s,

',s' s.

6 s

s '.

s

\\.

f.

a :

l t.

1

\\

a

\\\\e

/

\\

\\

~

\\

s.,

cv.

t t

t t

t t t I e a

t i

e t

t 1 iI t

t i

1 iI 1 A.

10 -2 ja -1 20 0 to 1.1 '.

s.

Periad (seconds)

Ng MEDIAN SPECTRAL 5HAPE5 H= 6. 5 (6. 0-7+), ROCK LEGEND HOR 120NR, M 6.52 (6.0-74), D:6.09 m (0-10 21, AVC PGA 0.456 G, 28 REC.

HORIZONTAL, msg.36 (6.0-741, D*26.47 m (10-50 m), AVC PGA

• 0.124 C, 206 REC.

• • =*

VERTICAL, msg.52 16.0-74). D:6.09 m 10-10 21, AVC PCA : 0.457 G, 11 REC.

VERTICAL, rt:6.3616.0-74), D:26.47 m (10-50 m), AVC PCA = 0.074 C,103 REC.

i l

Figure 21. Median statistical response spectral shapes (595 damping) computed from WUS data recorded at rock sites in the magnitude range of M 6 to M 7+.

Rupture distances range from 0 to 10 km and 10 to 50 km.

I

1 1

l',

w 1

i i

ie i e ii i

,,,i, e.;

p.

y t

'a

,,, y ; -

,~

~s s

.--J'

's>,,',

.s

',s l

- o

__a a

rs SN s s.s

\\

t.,s.'.

N%

s',

g

\\l

\\s.

M.

r.,,

L 4 7 i

a :

.s is.

s s.

's \\'.

\\s l.

.\\

'g

\\

I

\\\\

g

\\

\\

ev

\\

R 10 -2 30 -3 20 0 lb 1 L

Per iod (seconds )

l MEDIAN SPECTRAL 5HAPES i

M 5.5 (5.0-6.0), SDIL LGEND HORIZONTE., M 5.7615.0-6.01. D*7.80 KM 10-30 m), AVC PGA 8 0.263 C, 24 EC.

=***

L f

HORIZONTR., Ms5.59 (5.0-6.01. D 22.0E 101 (30-5010H, Avc PGA 8 0.320 G, 370 EC.

VDITICAL, M25.76 (5.0-6.01. Is7.90101 (0-101011, AVG PGA s 0.204 C, 31 REC.

WERTICAL., M:S.6915.0-6.0L 3:22.06 m (10-50 21, AVC PCQ s 0.069 G,194 REC.

I

~~--

(

(

F1gure 22. Median statistical response spectral shapes (5% damping) computed from WUS data recorded at soil sites in the magnitude range of M 5 to M 6. Rupture distances range from 0 to 10 bn and 10 to 50 km.

l L

~. -

i 4

j g

• ,',,.va.

, ", /

,.**.Qs'*s,N

=

1 s

'/

,s

.s

__ _ ;I ~' /-

'N s s cs R

's,N

~

,s s s s, s e,

's}

4 6

s J

'h g

\\'q\\

a, t

\\

\\

e,

\\ s.

e V

S :

s y

\\

=

p t,. -

\\\\ * -

h gs

\\'i v

~

is ~

7

,,,T \\

S l'0,.

0 10 10 -2 10 ~3 20

\\.

=

Per iod (seconds )

v ts MEDIAN SPECTRAL SHAPES M=6.5 (6.0-7.0), SOIL i,

LEGEND HORIZrNTAL, M 6.51 (6.0-7.0). D 5.56 2 IO-10 21, AVG PGA

• 0.381 G, 97 REC.

HORIZONTAL, Mr6.33 (5.0-7.01. D 28.49 m (10-50 21, RYG PGA 0.136 G, 505 REC.

VERTICAL, M 6.51 16.0-7.01, D 5.56 2 (0-30 m ), AVG PGA

• 0.315 G, 42 REC.

VERTICAL, M:6.3316.0-7.01, b28.49 KM (10-501011, AVC PGA = 0.089 C, 247 REC.

Figure 23. Median statistical response spectral shapes (5% damping) computed from WUS data recorded at soil sites in the magnitude range of M 6 to M 7+.

Rupture distances range from 0 to 10 km and 10 to 50 km.

m..._

..m.

I l.

t.

I l

l 4

1 4

f e.,.

g

=

a

~h b

2!

's.

I LISta3 i

8 E. ese asca evgenst af si sentrastE senPwats 8 5. 8as 8084a A988888 SF G 810A!Itu1E 88EPedt318

• aa 9

18 '8 34 *4 19 e gp a teled deseenees I

l 418(:0 l

6 E. IBA Rotte avgaaet y 33 m133r1E tenPegguts

$ !. $ms Asta avtaa33 0F f W110NTE C04PtetN18

,, '.l j.

e -j' 2

'. / *.'.

l

\\

'\\

i

\\

i

\\,

i T

e "Is '8 at *8 80 e gg i e,s., i.eew.

Figure 24. Average 5% damping sesponse spectral shapes (Sa/a) computed from motions recorded on rock sites at close distances to M = 6.4 earthquakes (top figure) and M = 4.0 canhquakes (bottom figure). In each Sgure the solid line corresponds to motions recorded in WNAs dashed line to motions recorded in ENA.

I i

t

l l

,,...3 m :

~

EGDtD 5

NORIZONTR., PGA 0.495 G-3

~

~...

5 VCRTICAL, PGA

• 0.408 G i

o e !

n m

e tn 7

=

E 5.

~.

a 10 -2 to ~3 10 0 30 3 Per iod'- (seconds )

M = 6.5, ROCK D = 5 KM g :

gcoe 5

anzonrm., PGA 0.395G;

.*=.5 VCRTICAL, PGA 0.3B4 G

=

o ;

e"

.cln e,

e tn R

E 5

y a

10 -2 30 -1 30 0 so 3 Period (seconds) i I

M = 6.5, SOIL D = 5 KM Hgure 25. Median empirical response spectra (5% damped) computed at rock and soil sites for M 6.5 at a fault distance of 5 km.

i o

~

s u

-a

--.y na.

, +..

s g

~

LEGEND

(

R 1 Kn R

5 Kn R: 10 KM i

.0 R s 20 KM Y

R=Cm e

m A

7 T

• S g

%A x

0 M 6.5,

ROCK, WNA EMPIRICAL V/H RATIO a

to -2 10 -1 la D 10 1 Per iod (seconds )

g WGEND i

R = 1 KM 2

R=5Kn I

R = 10 m

~

~

R=Em R=42 C

M M

o

$" L

'A%

g X

M 6.5,

S0IL, WNA EMPIRICAL V/H RATIO a

10 -2 go -1 lo o go i Period (seconds) l Figure 26. Distance (fault) dependency of response spectral ratios (V/H) for M 6.5 at rock and soil sites. Line at 0.66 indicates the constant ntio of 2/3.

i M

B B

5 s

p p e a a s

e a

3 s g s v I

1 4

4 i3 s o

l trGEND M = 5.5, D:1 KM

(

M

• 6.5. D:1 KM M = 7.5, D 1 KM M = 5.5, D:20 m a

n 6.5, D*20 m

.e*

M = 7.5, D 20 m e

=

o ea u

=_____

~.

t:

. ~~.~....--

y

. - - - = _

MEDIAN SPECTRAL RATIOS (V/H)

EMPIRICAL, ROCK e

10 -2 ja -1 10 0 to 1 Period (seconds) g LEGEND

.C M

5.5, D

• 1 kN

)

M 6.5 D 1 KM M s 7.5, D 1 XM M = 5.5. D = 20 KM

,o M = 6.5 D 20 KM e

M 7.5, D = 20 KM s

• • b,

_a ea.----- y 3

o o

g

%M...- '.

~

MEDIAN SPECTRAL RATICS (V/H)

EMPIRICAL, SOIL sa 10 -2 ja -3 10 0 to 1 i

Period (seconds) 1 l

l Figure 27. Magnitude dependency of response spectral ratios (V/H) at fault distances 1 and 20 km.

i l

)

l l

I i

I

.....3 a

2 :

i i

t a

o i

n i

cn l

e t,n T

a E

LEGEND 3

5 LUC DATA s x, un nocct q

R 10 -2 10 ~3 10 0 10 2 l

Period (seconds)

LANDERS, VERTICAL LUC

.....3 o

a l

o L

o :

m en l

w l

e m

7 a

i LEGEND a

5 %,

LUC DATA 5 x, Luc noott t

7 a

10 -2 30 -1 10 0 30 3 Period (seconds)

LANDERS, HORIZONTAL l

LUC Figure 28. Comparison of simulations to recorded motions for vertical and horizontal (average) mmponents at the SCE rock site Lucerne for the 1992 M 7,2 Landers earthquee. The site is at a fault distance of about 2 lun. A point source model is used with the generic roca compression. and I

shear wave velocity prontes (Figure 1) over the regional crustal model (Wald and Heston,1994).

l i

r I

n R

ueD R s 1 Kn

~

n k

R s 5 Kn R

10 KM R s @ KM

.O R = 40 KM e-e o

A

• S 7

.+

g g

M 6.5,

ROCK, WNA EMPIRICAL V/H RATIO 7

a 10 -2 10 -3 10 0 to 1 Per iod (seconds) g weD

~.

D

• 2 Kn I

D 5 KM N>

D: 10 KM

~

~

DsM2 0

Da em

-d=

m 5" [_

B M.6.5,

ROCK, WNA MODEL V/H RATIO g

10 "2 to -1 to 0 to 1 Per lod (sec)

Mgure 29. Comparison of empirical and model response spectral ratios (V/U) at rock sites for M 6.5.

l

e uaD n

R s 1 Kn

(

R

• 5 KM 3

R

• 10 KM R:Em R

• 40 Kn cm y

~

~

M 6.5,

SOIL, WNA EMPIRICAL V/H RATIO o

10 ~2 to ~3 10 0 10 1 Period (seconds) 2 :

acD

_(

D 1 KM D : 5 Kn D s 10 KM

.3 D

2 KN T

D = 40 KM e

a 3

~

M 6.5,

SOIL, WNA MODEL V/H RATIO y

E 10 ~2 10 "I 20 0 30 1 Per lod (sec)

F1gure 30. Comparison of empirical and model response spectral ratios (V/H) at soil sites for M 6.5.

i d

i t

.t L._________,

L_....,

I c

I 1

e l

A l

l 8

i 8

i a

e i

i l

l l

l 8

l Ev M

e ss i

0 0

5 l

Q.

l b

I l

ui i

e I

I t

u:coe

_l os l

l f

14 5 l

CEUS t

i cas l

I g

I i

,I i

l O

i s

O.

1.

2.

3.

4 5.

G.

7.

Vs AND Vp VELOCITIES (KN/SEC)

GENERIC WUS AND CEUS l

i CRUSTAL MODELS Figure 31. Comparison of generic compression and shear-wave velocity profiles for WUS and CEUS crustal conditions.

l

i

~

g.,...

o

)

LEGEND k

D 1 KM.

3 D s $ KM D: 10 KM c

D N KM.

.c D = 6 KM x

c 5" :N N

1 i M 6.5,

ROCK, ENA MODEL V/H RATIO 7

a 10 -2 to -1 to O to 1 l

Per iod (sec) i e

trcenD D8 1 XM l

(

Dx$KK i

3 0 m to XM D : 20 KM

.3 D e 40 KM e

A I" Vm NNM i

0 V

'M 6.5,

S0IL, ENA MODEL

~

T V / H, R A T,I O,,,,,

a 10 -2 3a -1 to O to 1 Per lod (sec)

Mgure 32. Response spectral ratios (V/H) computed for CEUS rock and soil sites for M 6.5 at a suite of distances. 'Ihe CEUS crustal model (Figure 31) is used for rock sites with the generic soil profile (Figure 2) placed on top to model soil sites.

4