ML20235T446

Earthquake on 860131 Near Chardon,Oh & Significance for Perry Nuclear Power Plant & for Earthquake Hazard in Eastern Us.* Testimony Before Subcommittee on Energy & Environ

ML20235T446
Person / Time
Site:	Perry
Issue date:	04/08/1986
From:	Seeber L COLUMBIA UNIV., NEW YORK, NY
To:
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CON-#189-8098 2.206, NUDOCS 8903080287
Download: ML20235T446 (19)

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s THE JAN 31,1986 EARTHOUAKE NEAR CHARDON, OHIO AND ITS SIGNIFICANCE FOR THE PERRY NUCLEAR POWER PLANT AND FOR

/G EARTHOUAKE HAZARD IN THE EASTERN U.S.

i Testimony Before Subcommittee on Energy and the Environment Committee on Interior and Insular Affairs United States House of Representatives April 8,1986 -

Washington, D.C.

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Leonardo Seeber Associate Research Scientist Lamont-Doherty Geologica10bservatory of Columbia University Palisades, New York 10964 8903080287 860408 PDR ADOCK 05000440 G PDR 3 503 p *, t\ 5 L O p

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INTRODUCTION AND MAJOR POINTS I address you today as a scientist who, for a decade has been focusing his research on seismicity and earthquake hazard in the eastern U.S. Several disciplines are involved in the understanding of earthquake hazard, ranging from the study of active geologic processes and the generation of earthquakes, to the generation and propagation of seismic waves, and to the effect of earthquake vibrations on man made structures.

My professional interest and expertise resides primarily on the O

b earthquakes as a manifestation of the neotectonic regime, Following are the major points in my presentation:

1. Preliminary results from the study of the January 31,1986 Chardon earthquake suggest to me that the earthquake hazard at the plant may be higher than originally thought, but this hazard remains very uncertain and can still be considered similar to the hazard at many other plant sites in the eastern U.S., even ones that have not experienced such a nearby earthquake.

2. The Jan 31 event, unexpected by lay people and scientist alike, reinforces the growing awareness that earthquake hazard in the eastern U.S. may be substantially higher than is generally perceived, in relation to the safety of nuclear power plants as well as many other structures.

3. Tne Jan 31 event underscores the need for continued earthquake g monitoring and research near the Perry Plant and, generally, in the eastern

(, ) U.S. This research is a long-term investment which will provide the basic information for decisions on a variety of engineering pro'lems. a The wisdom of such an investment is in sharp contrast with the current plan by the Nuclear Regulatory Commission to discontinue its earthquake monitoring program. This program has been the main source of support for research on eastern earthquakes by the universilles and is responsible for much of the progress during the last decade.

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. 3 PRELIMINARY RESULTS ON THE AFTERSHOCK SEQUENCE OF THE CHARDON, OHIO EARTHOUAKE, JANUARY 31,1986 AND SOME IMPLICATIONS -

The January 31,1986 Mbig 5.0 Chardon, Ohio earthquake was centered 40 km east of Cleveland and 17 km south of the Perry Nuclear Power Plant (Figure 1). This earthquake was widely felt, caused scattered light damage ,

in the epicentral area, mostly in the form of broken chimneys and fallen I

objects, and caused high acceleration at the Perry Plant. Aside for its proximity to the Perry Plant, this earthquake is particularly noteworthy beCause:

1. It occurred in an area of relatively low seismicity, outside any )

recognized seismic zone and is a representative of a class of " unexpected"  !

events which are of particular concern in the eastern U.S.;

2. It is characterized by very few af tershocks, a possible symptom of persistent high stress and earthquake potential;

3. It may possibly have a cause and effect relation to two type I deep wells for waste disposal on the basis of their proximity to the ,

epicenter (about 12 km) and the large amount of fluid (about 300 million gallons) injected since the early 1970's.

Aftershocks A substantial aftershock monitoring effort involving many institutions and seismologists, including the Lamont-Doherty Observatory, was carried out for a month af ter the main shock. At least 10 af tershocks 1 ranging in size from Mc=2.5 to Mc=-0.5 were recorded Our preliminary results from the study of these aftershocks suggest a rupture striking north-northeast, centered at a depth of about 6 km and about i kr'n wide (Figure 2). Fault-plane solutions for the aftershocks suggest a predominant right-lateral strike-slip displacement on the preferred fault i plane (Figure 3) and are consistent with the northeasterly directed axis of ,

l maximum horizontal compression which cheretterizes the regional stress I field (Figure 4).

Hypocenters of the aftershocks following the Jan 31 event are located approximately around the circumference of a vertical circle (Figure 28). Similar af tershock distributions were found for the Octo' 'r 7, ,

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Figure 1: Epicenter of the January 31,1986 Chardon earthquake located about 30 miles east of Cleveland, Ohio. Downtown Cleveland is near the western edge of this figure. Also shown is a possible configuration for a network of six seismic stations that could monitor long term seismicity in the epicentral area.

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by several institutions. Filled circles indicate af tershocks during tua firsty week of the sequence. Hypoinverse error bars are shown.

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i Figure 3A: Preliminary fault plane solution for the February 3 aftershock, )

Mc=2.1, of the January 31,1986 Chardon earthquake. Upper hemisphere j projection, filled circles are compressions and open circles are dilatations.

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Armbruster and Seeber, L-DGO, PRELIMINARY RESULT-3/25/86 Figure 3B: Preliminary fault plane solution for the February 6 aftershock, Mc=2.5, of the January 31,1986 Chardon earthquake. Upper hemisphere projection, filled circles are compressions and open circles are dilatations.

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centered near the January 31,1986 epicenter (Hildenbrand and Kucks,1984). ,

The cross indicates that epicenter and the long arm on the cross indicates the .

direction of the inferred fault (the length of the rupture is about I km,much .

smaller than the arm of the cross at the scale of the map). The small arrows ),

Indicate the direction of slip inferred from the af tershocks. This slip

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Sf compression in the regional stress field (large arrbws). The inferred f ault is i . ,

3 also aligned with a major boundary in the magnetic fleid which may reflect a existing tectonic boundary in the basement. P Indicates the site of the f

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Figure 5: Hypocenters of well recorded af tershocks of the October 7, )

O 1983 Goodnow earthquake in the central Adirondacks during the first 4 days of the sequence. These hypocenters are confined to a narrow planar zone which is viewed f ace on in this section. The circles give the range in rupture dimensions inferred from modeling the short period teleseismic P wave of the main shock recorded at many stations worldwide. The ci,rcles are centered at the hypocentral depth inferred from the moment tensor inversion (8 km). These results indicate that the af tershocks are confined for the most part to the outer edges of the rupture where stress is probably concentrated.

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V Armbruster and Seeber, L-DGO Figure 6: Seismicity associated with the October 19,1985 earthquake near Ardsley, Westchester county, N.Y. Hypocenters are plotted in map view (right side) and on a section parallel to the inferred rupture plane (Indicated on map; view is from the southwest)

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1963 Ms-5.2 earthquake in the central Adirondacks (Figure 5) and for the -

October 19,1985 Mbig=40 earthquake just north of New York City (Figure i 6) The af tershocks are probably concentrated around the edges of the -

I ruptures associated with the respective main shocks. The ruptures of these eastern earthquakes, then, are small compared to representative western events of similar magnitudes and are characterized by relatvely high stress-drops. This result implies that similar size faults can produce larger earthquakes in the East than in the West and that an earthquake substantially larger than the one on Jan 31,'86 can be produced by a f ault only several km across. Such a fault could be easily undetected by geologic y or geophysical investigations.

Ruoture Geometry and Large Scale Features in the Basement l

Data on the main shock will be available from seismic stations ]

worldwide. Important characteristics of the main shock, such as the j moment release, the fault plane solution and the displacement across the i rupture will be derived from these data. Figure 4 shows magnetic intensity for eastern Ohio. These data reflect characteristics of the Precambrian l basement rocks in the seismogenic depth range (upper crust).

Superimposed on this map are the approximate direction of the highest compressive stress inferred from other studies (large arrows) and the January 31,1986 epicenter, indicated by a cross. The longest arm of the I

(' cross is in the direction of the fault plane inferred from the aftershocks.

\ The small arrows indicate the sense of movement on the fault inferred from the af tershocks. The geometry of f ault motion is consistent with the direction of maximum compression.

Figure 4 also indicates that the interred fault rupture is aligned with a major boundary in the magnetic map that separates a region of high magnetic relief to the northwest from a region of low magnetic relief to the southeast. The magnetic data in the area of figure 4 and elsewhere in the eastern U.S. Indicate other prominent lineaments or boundaries between distinct magnetic domains which probably reflect lithologic domains in the Precambrian basement. Some of these boundaries extend over large distances and may be controlled by faults. The Jan 31, '86 earthquake rupture coincides and is aligned with one of,these features. The dimension of this rupture Inferred by the distribution of aftershocks (Fig

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2), about 1 km across, should be contrasted with the length of the -

magnetic lineament.which can be traced for many tens of kilometers. If this feature was a capable fault, much larger earthquakes than the one on Jan 31,'86 could be expected on this fault.

l Many Precambrian tectonic boundaries of regional scale have been Inferred from magnetic data throughout the eastern U.S. The significance of these ancient features in terms of earthquake hazard, however, is not clear. In the Adirondacks, for example, where the Precambrian basement can be studied at the surface, these features are often found to be major ductile faults of Precambrian age with little evidence of younger O

reactivation as brittle faults. Some of these major ductile faults clearly control the spacial distribution of seismicity, but the ruptures in individual earthquakes are often on other faults with different orientations. <

The relationship between preexisting structural features 'and seismicity is a major topic of current investigations. Preliminary results suggest that major tectonic boundaries in high grade terranes may control the distribution of earthquakes without becoming reactivated. Thus, the alignffnent of the Jan 31,'86 with a regional magnetic lineament need not ,

imply that the lineament is an active fault with the potential for large '

earthquakes. The hypothesis of a large active steeply dipping fault in the basement is not easily reconciled with the lack of evidence for such a fault in the Paleozoic . sedimentary cover, where detailed structural control is available from well data. In conclusion, the correlation between O earthquake and magnetic data in our preliminary results and its significance need to be thoroughly investigated, at this stage, a major active fault seems very unlikely when other factors are taken into {

account, but the possibility that the same fault that produced an Mbig=5 l earthquake on Jan 31 '86 will produce larger ones in the future need,s to be {

considered.

Continued Aftershock Monitoring Continued high-resolution monitoring of the epicentral zone of the Chardon event is essential. More af tershocks are likely, considering that the 1983 Ms 52 earthquake in the Adirondacks v(as followed by an af tershock sequence that lasted for at least 1.5 years. This monitoring can l.

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provide prompt and precise information on any significant event to I concerned public officials, power company managers and the general public. It may also establish whether the seismogenic fault is producing microearthquakes outside of the immediate 1986 rupture area and if the activity is migrating to other portions of this fault. Continued monitoring may also test the hypothesis that at least some of the seismicity in the Chardon area is induced by high pressure injection of fluids in deep wells.

The results which will be obtained from the study of the aftershocks and of the main shock will be useful, but certainly not sufficient to answer O the many important questions about earthquake hazard which were raised V by the Chardon event and which are generally of concern in the eastern U.S.

GENERAL. LEVEL OF HAZARD IN THE EASTERN U. S.

Tae fallacy of many assumptions underlying previous estimates of earthquake hazard and the need for revisions, generally upward revisions, of the hazard estimate in the eastern U.S. are now widely acknowledged, but reliable new estimates of this hazard are not yet available because basic questions about the seismogenic process remain unanswered. Some of the items contributing to this hazard and to the low level of awareness for it are.

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1. The level of hazard as meBSured by the average rate at which area of intensity Vill (substantial damage) or greater was produced by earthquakes during the historic period is about the same in the eastern as in the western half of the U.S. Most of this area of potential damage in the eastern U S. was produced by few large earthquakes, all in the previous century, before seismic instrumentation, before any living memory, and before the numerical and technological expansion of society (Figure 7).

2. Very little is known about where and how of ten these very large earthquakes with such potentially catastrophic consequences may occur again. Historic data on pre- ins @ mental seismicity indicate that the Coastal Plain of South Carolina was not experiencing a relatively high level of seismicity before the 1886 Charleston earthquake (Figure 8).

Moreover, recent data on structural features in sediments generated by strong shaking suggest that,large prehistoric earthquakes similar to the

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7 one in 1886 have occurred in the southeastern Coastal Plain in places other than Charleston. These results suggest that very large destructive earthquakes may occur in places other than the historic sources of such events and that the site of the next large event may now be experiencing an average level of seismicity.

3. Much of societal infrastructure in the eastern U.S. was built under the assumption of unrealistically low earthquake hazard and a similar level of shaking can be expected to cause more damage in the East p than in the West.

Q/ 4 The application of hazard mitigation measures in the East may be handicapped for some time by lack of knowledge derived from the ,

relatively low emphasis on earthquake research in this part of the country.

NEED AND PROSPECTS FOR EARTHOUAKE RESEARCH IN THE EASTERN U. S.

Generally, the 1986 earthquake in Ohio underscores the importance of earthquake studies in the eastern U.S. at a time when substantial cuts in this research effort are being considered. The nature of seismicity and n

v intraplate tectonics in the eastern U.S. are poorly understood, but a significant level of hazard can be deduced from the data Given that the Jan 31, '86 earthquake exceeded design accelerations at the newly constructed Perry Plant, any expert opinion on where disastrous earthquakes can and cannot occur should be regarded with skepticism. Such a low level of understanding about eastern selmicity is not surprising '

because a substantial commitment to studies on eastern earthcluakes, l

including monitoring by seismic networks, is a recent development. The Jan 31 '86 earthquake makes it clear that a sustained commitment to this research is necessary.

Wnile the influence of earthquake ground motions on the Perry nuclear power plant and the possible triggering of the January 31 earthquake by fluid injection are questions of immediate and criticafimportance for the Cleveland area, there are issoes of national concern that are also raised by

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5 the occurrence of this earthquake. Four events with magnitudes about 5 or greater occurred in the northeastern U.S. and adjacent Canada during the last decade. The 1980 Kentuky earthquake, the 1982 New Brunswick - l l.

earthquake, the 1983 Adirondack earthquake and the 1986 Ohio earthquake.

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i Except for the 1983 event, these earthquakes surprised the seismological community by occurring outside recognized and well monitored seismic zones. Clearly there is a danger that stems from the phenomenon itself and from the poor level of understanding The major federal program that has supported the gathering and the O study of information on earthquakes in the eastern U.S. has been funded through the Nuclear Regulatory Commission (NRC). This agency has announced that it intends to stop all of its support of seismological monitoring in mid-1987. The NRC has been responsible for most of the monitoring of eastern U.S. seismicity, providing major support for networks of recording stations in the northeast, southeast and midwest.

f1ost of the monitoring program was carried out in cooperation with universities, where the NRC program also supported the use of date obtained by the monitoring in research about the causes and effects of '

eastern earthquakes.

The end of the NRC support for earthquake studies would leave a major hole in the fabric of the research effort to determine ard mitigate earthquake hazards in the eastern U.S. The compilation of earthquake catalogs, essential to evaluating the temporal and spatial distribution of ,

O seismicity, will be severely curtailed. The gathering of basic information on ground motions, necessary to evaluate the effects of earthquakes on structures, will be ef f ected 1 Wnile the continuation of the monitoring program is essential to the ability to evaluate the risk from eastern earthquakes, the end of the NRC program would have an equally dekstating impact on the support of research into the causes of eastern earthq{akes. We cannot promise that recording of earthquakes will necessarily gd to an ability to predict the exact time of future earthquakes, but we can be sure that without establishing a complete earthquake catalog, there is little hope of ever being able to predict future earthquakes. We can be sure, however, that a )

careful program of earthquake monitoring and research will le) to significant improvements in public safety through' improved building practices and siting procedures. Fundamental data on earthquake

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I occurrence and earthquake effects are required for these improvements.

These fundamental data include catalogs of earthquakes - to document the spatial and temporal distribution of seismicity - and recordings of ground motion on different rock types from different size earthquakes - to '

determine the ground shaking to be expected in different siting environments. While most of the world is moving forward, increasing the effort on earthquake hazard studies, the eastern U.S. would be moving backward.

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