ML20133G082
| ML20133G082 | |
| Person / Time | |
|---|---|
| Issue date: | 06/13/1983 |
| From: | Beratan L, Murphy A, Schmitt T NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Arsenault F NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20132B198 | List: |
| References | |
| FOIA-85-363 NUDOCS 8508080550 | |
| Download: ML20133G082 (7) | |
Text
-_ _ _ - _ _ _ _ . _ _ _ . _ _ . _.__ _ _ _ _ . _ _ _ _ _ _ _ _ . _ _ .
Y- .3 .k /. n G.
JUN 13 gg3 1
NEM0RAN0tM FOR: Frank J. Arsenault. Director Division of Health. Siting and Wasta Management. RES FR21: Leon L. Beratan. Chief Earth Sciences Branch Division of Health. Siting and Waste Management. RES .
Andrew J. Murphy Leader Seismology Section Earth Sciences Branch Division of Health. Siting and Waste Management. RES Thomas J. Schmitt. Geologist Seismology Section _
Earth Sciences Branch Division of Health. Siting and Waste Management. RES b..
Ernst G. Zurflueh Geophysicist '
Seismology Section Earth Sciences Branch Division of Health. Siting and Weste Management RES
SUBJECT:
TRIP REPORT ON 'THE WORKSHOP ON THE 1886 CHARLESTON EARTHQUAKE AND ITS IWLICATIONS FOR TODAY.* MAY 23-26,1983 We recently attended the " Workshop on the 1886 Charleston Earthquake and its Implications for Today." held near Charleston. S.C. on May 23 through May 26 l 1983. A meeting agenda and list of attendees is attached. The formal objectives of the workshop were:
- 1) To define the state-of-knowledge of the 1886 Charleston earthquake in the context of eastern seismicity.
- 2) To identify and discuss the most important scientific, technical, and societal issues arising from the 1886 Charleston earthquake and their implications with regard to research, earthquake-resistant design of buildings and critical facilities, earthquake hazards reduction, preparedness, in the Eastern United States.
(', 3) To recomend research and implementation actions to resolve the most important issues,
' *"*"*
"" "( . . BELL 85-363 PDR 4.. . .p . . j. .
OFilCI AL RECORD COPY ac oav ne no soi nace one 3[
Frank J. Arsenault ,,
- 4) To identify possible resources for future research and implementation actions. and
- 5) To review and evaluate current ongoing research.
The Workshop connenced at approximately 5:00 p.m. with a welcoming statement by N. Olson of the South Carvlina Geological Survey who introduced Walter Hays.
USGS, who served the function of Workshop Chairman. Following Mr. Hays's connents of the scope and objectives of the Workshop, representatives of the various sponsoring agencies addressed the participants including your own connents.
4 In.ediately following the welcoming session, the first plenary session was held to help set the stage / tone for the workshop. Three geoscientific and one "pubite awareness" papers were presented in this session. Connents on the presentation by L. Seeber will be made later. O. Nuttli presented a paper recounting both a scientific and " journalistic" description of the earthquake and describing the potential effects of a modern recurrence of the 1836 Charleston earthquake. He particularly noted the potential for significant motion in the upper levels of medium to tall buildings in cities such as Atlanta, Boaten, Chicago, New York and St. Louis--
Atlanta, MM intensity VIII-IX and; Washington, MM intensity VI-VII. T. Algermissen reported on some preliminary sensitivity analysis of probabilistic ground motion -
calculations to assumptions about the tectonic hypothesis used (this work partially supported by the NRC). He also noted as a personal opinion that improvement of the Eastern U.S. attenuation models would have more impact than seismogenic source Q' zone changes.
An interesting paper was presented by Risa Palm entitled, " Improving Hazard Awareness." No further connents or descriptions will be given in this trip report on the "public awareness" aspacts of this workshop.
During the evening session C. Thiel and J. Nigg presented a description of the potential physical consequences of a recurrence of the Charleston earthquake.
The Workshop participants had been previously divided into three groups and were assigned roles to play which varied from reporters OMP officials, Civil Defense coordinators, etc. In these various roles the participants were asked to respond to various questons and situations. The results were tabulated and presented later in the Workshop. Overall it was a very fascinating and infonnative exercise.
, The first technical session was entitled, " Eastern Seismicity with Emphasis on the i
Charleston Earthquake-Progress, Problems, and Competing Hypotheses." The session Chainnan, Paul Pomeroy made some opening remarks and asked that each of the session penelists address the following points or questions during his presentation:
(
=c ,omo n..io..o. ac" " OFFICIAL RECORD COPY
Frank J. Arsenault f 1 Is there a preferred tectonic model for the Charleston earthquake?
2 How unique are any of the models?
3 What pieces of evidence are most conclusive?
4 What evidence would be conclusive regarding either the question of causative mechanism or the question of uniqueness?
L. Seeber presented a paper describing the back-sliding-on-a-decollement model j particularly emphasizing a new set of earthquake epicenters located via felt
! reports for a few years before and after the 1886 earthquake. He also presented a line of evidence indicating that the aftershocks for the 1886 earthquake ended j by about 1891-92. (This is an important conclusion which was supported by other presentations.) He did not take time to address the four points during his presentation; but afterwards in private conversation he indicated that
!' conclusive evidence probably does not exist but that critical geological / geophysical investigation should be able to detect extensional tectonics at the up-slope teminus of the decollement.
I C. Wentworth presented the reverse-faulting-in-a-compressive-regime hypothesis i
which he felt was supported by the " Charleston geologic evidence" but not by the current seismicity. He had no specific answers to the four questions but noted the need for more regional data to be gathered according to a preconceived ;
plan, b J. Behrendt reviewed his motion-on-faults-listric to the decollement hypothesis.
He listed the following experiments as most crucial: focal mechanism deteminations, current seismicity, and multi-channel seismic reflection profiles. P. Talwani discussed three models: stress amplification, e.g., plutons associated with
- seismicity, decollement reactivation or backsliding, and block tectonics. He seems to favor some combination of several hypotheses relying on the intersection of geologic elements with a significant role for the off-shore fracture zone and the spatial relation to current seismicity. G. Bollinger did not have a model or hypothesis that he was willing to endorse but felt strongly about the need for continued seismic monitoring and for continued collection and processing of seismic reflection profiles. He introduced the idea of suspect terranes to the participants--
relevant to the intersection of complimentary hypotheses.
N. Ratcliffe did not advocate a particular hypothesis but endorsed the concept of resolving some aspects of the Charleston problem by studying areas with similar geologic phenomena where it was possible to visually examina the basement rocks on the surface, i.e., the Ramapo fault system.
1
\
..c ron- n. , io .o . wc. o m OFFICIAL RECORD COPY l
. f.
Frank J. Arsenault r.
The second half of the first technical session placed emphasis on the role of geological and geophysical investigations in evaluation of critical Charleston hypotheses.
The need to view eastern seismicity in the context of regional stress, strain, structure, and rock mechanics was advanced by several panelists and discussed by sane participants. The possibility of establishing a coherent view of the eastern seismicity was supported by new data concerning the stress field of the Southeastern United States; that subject, and its interpretation and implication dominated the discussion of regional tectonics.
Mark Zoback presented data indicating that the stress field in the East is similar to that in the rest of the United States, that is the maximum compresstresstresst is oriented at about N50 0E. This is in apparent contradiction with the stress fieldininferrgd but a N50 Ebystress the Stafford field it would fault system.
be a strike TheslipStafford is a reverse fault. Several fault participants suggested that the Stafford was a strike slip fault with a reverse component.
Earthquake hypocenters in the Central Virginia seismic zone have been associated with structures defined by reflection seismic profiles. This is one of the most significant observations of seismotectonic in the East. John Costain discussed those results and how the results obtained there relate to investigations -
in the rest of the Eastern United States.
O setter hynccentrai iocations of earthquakes and fauit piane soiution to earth-quakes were considered critical to understanding the seismicity innediately in the Charleston region. This information will be obtained by planned upgrading of the Charleston seismic network to include broadband digital units.
It was the cunsensus that a deep borehole at Charleston is not advisable at present. There is no specific target for drilling. The most promising geologic investigations in the Charleston area at present are shallow drillings and itquefaction studies.
The next technical session that was significant to NRC/RES concerns was entitled,
" Role of Historical Seismicity vs. Tectonics as Indicators of Seismic Hazard "
A consensus seemed to develop that historical seismicity and tectonic models are not competing concepts but are complementary and must be used that way to make progress with the Charleston problem. L. Reiter reviewed some of the problems facing the NRC as a result of the Charleston earthquake and Appendix A to 10 CFR Part 100. J. Devine reviewed the significant growth in geoscientific knowledge as a result of the Charleston research projects. J. Dewey, who has spent a considerable arnount of time studying many intraplate earthquakes, described two tendencies and issued one warning.
b "C' ""''""C" "
0FFICIAL RECORD COPY
Frank J. Arsenault f*
- 1. Large mid-plate earthquakes sometimes occur at sites of previous large ;
mid-plate earthquakes within a number of decades.
- 2. Large mid-plate earthquakes sometimes occur at sites of only small previous earthquakes.
Warning: Some large mid-plate earthquakes occur at site of no apparent previous activity (several centuries).
R. McGuire described a series of strategies for addressing the Charleston problem: Worst Eerthquake, Waiting for Scientific Advances, Identification of Likely Candidates, and Reliance on precursory Seismicity. This was a very provocative paper on the cost effectiveness of the various strategies. There are problems associated with each strategy but a copy has been attached and it is strongly recommended for reading. For the next session the workshop broke up into four discussion groups, seismicity, geophysics, geology, and public awareness. Specific reports from the first two groups follow.
Seismicity. The two principal conclusions reached by the group are:
- 1. The current seismicity seen in the charleston-Somerville area is not aftershock activity of the 1886 earthquake.
- 2. The current seismicity is outlining a vertical feature. ,Thus, r: although a movement in 1886 on a decollement surface can not preclude, U the current seismicity does not support it.
The research efforts supported / discussed by the group include:
- 1. Improvement of the velocity model to define the feature or patterns of seismicity for correlation with geologic structures and to reduce the uncertainty in the focal mechanism-stress orientation.
- 2. Improvement in the network instrumentation and its spatial distribution to facilitate collection of ground motion and attenuation data, source parameter studies, and focal mechanism determinations.
- 3. To target specific areas for detailed study (areas were not specified).
- 4. Determination of A-values. -the portion of the recurrence relation that sets the absolute value of the recurrence relation.
?
v Datt k ............... .. ..................... ..................... ..................... ..................... * . . . . . . . . . . ............
neroa.u.oo...we.oua OFFICIAL RECORD COPY
~
1 Frank J. Arsenault 1 O
Geo W sics. Conclusions reached or opinions expressed in this discussion group
! inc'ude the following:
1
- 1. A wealth of data has been collected on eastern seismicity and tectonics.
What is needed now is a synthesis which uses the individual pieces j ' of infomation to define more clearly what the tectonic conditions 1 are that cause earthquakes, what the earthquake expectancy might be in I different locations and what further research is needed to fill gaps in the data.
t' i 2. A consensus was reached that the eastern overthrust (or decollement)
- is not the driving mechanism of eastern seismicity.
In investigations into the causes of this seismicity we are looking for specific zones with distinctive tectonic characteristics. Such a zone i could cause local seismicity by reactivating the overthrust locally cr by inducing some other type of fault motion. Conversely, eastern j seismicity is not based on a vague zone encompassing the eastern seabcard j with an equal earthquake probability at any point.
i 3. The Blake Spur fracture zone does not seem to continue onshore to connect I with the Ashley River fault, for instance. Magnetic and gravity maps do -
- not show evidence for this. However, in an earlier session Dr. Talwani l expressed the opinion that the Blake Spur fracture zone does continue
- (.) ,
onshore as far as Eastern Kentucky with offsets (?).
I j 4. The deep crusted and upper mantle structure in Charleston is not known
^i well. That infomation was important in understanding the seismicity of the New Madrid and Rhine Valley seismicity and may be a very valuable a direction in Charleston.
l During the final session, reports were presented by each of the discussion groups l
and some self-examination was conducted, l In susmary, the Workshop served its function of bringing together many of the people working on and concerned with the Charleston earthquake problem, of
- presenting the accumulation of significant technical data, and of exposing both j the major advances and shortcomings of that data. Significant progress has been
! made since 1975 in understanding the Charleston area and now may be the time to j focus closely on those experiments that can most quickly resolve the Charleston i problem or at least reduce the number of competing hypotheses.
i I
i
(-
emp .................. . ................... ..................... .................... .... ................ .................... ............... ..
- .cc ro w n..io.... a w on'* OFFICIAL RECORD COPY
...r:
1 Frank J. Arsenault -
It is necessary to achieve a level of closure among the various hypotheses, order priorities and develop a comprehensive synthesis of the various lines of evidence. Some effort has been applied in this direction but there are shortcomings. We may need a synthesizer less personally and professionally dependent on this program.
A Leon L. Beratan Chief Earth Sciences Branch, RES
/5 Andrew J. Murphy Leader Seismology Section Earth Sciences Branch, RES b _
Thomas J. Schmitt, Geologist Seismology Section Q Earth Sciences Branch, RES h
Ernst G. Zurflueh, Geophysicist Seismology Section Earth Sciences Branch, RES DIST:
Subj Chron Circ ESB RF LLBeratan AMur l
EG urflueh l
\,
, , ,, e , , ESB:DHSWM ESB:DHSWM ESB:DHSWM ESB:0HSWM AMURPHY:pr:f ITT"" "EZURF tBERATAN
- "*> ......d.sl.'...... .......)........... . . . . . . . . . . .. c}.11 . . . E. .M. -,. $.Z ."". .. ."
e.ne ) .6././.d.
. 83
........... . . . . . /.J.
.......... 3 6408Y
. ./.8 ..................... . .6]
. . . $. . . 8 3. .............. . ..
.c re: n. n o..o , oc" "
OFFICIAL RECORD COPY