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San Andreas Fault - Seismic[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: San Andreas Fault - Seismic
- From: Yank2002(--nospam--at)aol.com
- Date: Thu, 3 Sep 1998 02:13:10 EDT
WHERE ALONG THE SAN ANDREAS FAULT WILL THE NEXT BIG ONE STRIKE ? In 1995 the California Institute of Technology advanced a theory published in the Journal of Geophysical Research (and reported by the Los Angeles Times, April 21, 1995 [A3] and by Nature Magazine, May 18, 1995, p.191) that earthquakes in the Great Basin, in the Aleutian trench in the North Pacific and at other points along the Pacific tectonic plate contribute to the build- up of seismic energy in California's San Andreas Fault (SAF). When the seismic stress level of the fault reaches certain "built-in-slippage-resistance-value" (historically > M7.0), the release of accumulated energy follows. According to some noted seismologists just the opposite to the Caltech assertion is true. The "seismic gap" theory postulates that over the long run all parts of the San Andreas fault must average about the same level of movement per time. This can happen either through the cumulative efforts of a large number of small earthquakes, or through rarer larger earthquakes, as happened for the part of the fault around Loma Prieta. A large and longstanding "seismic gap" is interpreted to mean that a significant earthquake should be expected. In order to find out how seismology professionals and individuals who could be affected by earthquake events might (or should) look at the issue, the IBM- compatible computer program developed by our engineering group generates maximum and minimum (and anything in-between) seismic energy accumulation from past earthquakes at any geographical location along the San Andreas fault - thereby satisfying both Caltech and Gap theories. Since current building code requirements do not adequately protect human lives and properties located in areas identified by geologists as high risk areas (1989 Loma Prieta, 1994 Northridge), this energy accumulation methodology exposes geographical segments along the full length of the San Andreas where "as per code design" of structures is not adequate, therefore, it is not safety-acceptable. Structural engineers, geologists, earthquake insurance underwriters; and other governmental or non-governmental entities involved with earthquake issues, might want to study the program to find out which geographical areas are the most vulnerable to these kinds of catastrophic events and consequently, whether the program could be of any benefit to them. The data for "SAF Seismic Stress Build-up Generated by Past Earthquakes" program was obtained from "Earthquake History 1769 - Present (California, Nevada and Baja California)" published by US Geological Survey in 1995. The program calculates and shows how releases of seismic energy at minor faults could affect the long term accumulation of energy in the San Andreas. Significant earthquakes (magnitude 5.0 and higher) from both sides of the fault (Pacific plate and North American plate) between 1906 and 1995 were entered into the program. The program user is invited to arrange / rearrange the most current earthquake data in order to find out what is today's seismic energy build-up at any geographic location long the fault. The structural engineer is the primary and final decision maker as to how the structure he has engineered will behave under seismic loading condition anticipated by applicable codes versus under more stringent "local" design requirements obtained from other sources (such as the SAF-computer program). The engineer has the responsibility of investigating the situation and making the owner of the structure, the design approval authorities, and the public aware of the fact that "as per code design" of a particular structure or a group of "local" structures (existing or new) might not be adequate. For geologists the program can also serve as an unlimited record-keeping vehicle where predetermined program participating or non-participating earthquake data is stored, calculated and displayed numerically and graphically, arranged either chronologically or geographically, or both. The information generated by this program could also be of interest to organizations such as: CA Department of Social Services - Disaster Response; CA Office of Emergency Services; Caltrans, Division of Structures; CA Seismic Safety Commission; FEMA, earthquake insurance underwriters and other individuals or organizations involved with earthquake hazards. To download a fully operational version of the program FREE OF ANY CHARGE please connect to our new Web-site: http://www.ES-SYSTEMS.NET and click on "San Andreas". (There are positively no computer viruses of any kind on our site). NOTES 1. Due to the complex nature of the program, it is necessary to have a reasonably thorough understanding as to what the program does and why before submitting any EMail inquiries to us. For this purpose a file-attached abbreviated documentation SAF-DOC.TXT (in ASCII format) is provided. The inquiries can be submitted to: Yank2002(--nospam--at)AOL.COM or Yank(--nospam--at)ES-SYSTEMS.NET. Please do not use SEAOC-server for these communications. 2. The SAF-program is a computerized-format mathematical and graphical translation of Caltech/Gap theories inquiring which communities along the San Andreas will be influenced the most by the major energy release in the San Andreas fault caused by prior seismic energy releases of minor California faults. 3. The program's database contains earthquakes of Richter magnitude 5.0 and higher arranged in the chronological order. If the user wishes to obtain a more precise reading for a particular locality, the database should also include earthquakes of magnitudes lesser than 5.0 for that specific locality. Depending on the required precision, a "local" segment of the fault will have to be isolated and expanded to reflect the inclusion of lesser intensity earthquakes for a chosen scenario, and for any time-period. The number of "local" segments the program can generate is unlimited. Example: In order to obtain a more precise reading for (say) San Luis Obispo, the database of the program should include the required data from participating earthquakes lesser than magnitude 5.0. The decision as to the range of earthquake data to be added to the database (say, M4.0 to M4.9 or M4.6 to M4.9) is entirely the user's decision. If such earthquake data is not readily available, the best source for the data is US Geological Survey: The address is: http://quake.wr.usgs.gov/more/eqhistory.html or the request for specific information should be directed to: webmaster(--nospam--at)quake.wr.usgs.gov. If there is not enough space in the SAF-program database to accommodate the additional data, some "non-participating" earthquakes positioned outside the longitude block from W119.5 to W122.00 degrees have to be temporarily deleted. (See "Step by Step Procedures" of the documentation). 4. The program does not pass any judgement with regard to the pertinence of the theories in connection with tectonic plate movements along the California coast and does not encroach onto the geology aspects of either theory. 5. Since a great number of nature-related catastrophic events affecting human lives (volcanic eruptions, hurricanes, floods, earthquakes) seem to occur as random incidents, the mathematical or projection-based forecasts for many of them are impossible or difficult to establish. The SAF-program is the best attempt of science to project earthquake events based entirely on "past performance criteria". 6. If the program was in existence in 1988 it could have pinpointed the "out- of-ordinary" level of seismic energy accumulation to the vicinity of the Loma Prieta earthquake location.
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