Issues

As this issue of Seismological Research Letters goes to press, the United Nations General Assembly has adopted a Comprehensive Test Ban Treaty (CTBT) that calls for the end to all testing of nuclear weapons. This international treaty will be the culmination of a process that has been closely intertwined with seismology, both research and funding, for more than a generation. A great goal of seismology has been reached, one that will clearly have a direct impact on the well-being of society.

With this major milestone in the history of seismology, it is appropriate to reflect on our roles and responsibilities as publicly-funded scientists. We hear increasing questions about the relevance of science and the need for federal support of basic research. As a community of research scientists, we must develop ways to bring our science to the public and convince them that basic research in seismology is worthy of...

INTRODUCTION

Small, shallow earthquakes induced by quarrying operations, petroleum production, and mining have been recognized in many parts of the world (Richter, 1958, pp. 155-156; Pomeroy et al., 1976; McGarr, 1991; Nicholson and Wesson, 1994), and they have been commonplace at a diatomite quarry in Lompoc for about 50 years (Yerkes et al., 1983). In the cases of induced earthquakes that involve removal of rock or fluid, rather than injection of fluid or superposition of a load, the cause of the earthquakes is generally attributed to decrease of the load stress and consequent increase of the shear stress leading to slip failure on an existing fault or bedding surface. The earthquakes at the Lompoc quarry are significant to understanding earthquake mechanics because they illustrate this process of coseismic rock failure at a scale that is intermediate between laboratory bench experiments and damaging, crustal scale earthquakes.

At about 11:30 PST on...

INTRODUCTION

The use of waveform inversion schemes for kinematic analysis of the seismic source has increased dramatically in recent years. These schemes have been used to examine in detail the spatial distribution of coseismic slip on the causative earthquake fault. The studies involve either a linear or a non-linear inversion of the seismic body waves to model the rupture history on a prescribed fault of finite extent (e.g., Hartzell and Heaton, 1983; Kikuchi and Fukao, 1985; Yoshida, 1986; Fukuyama and Irikura, 1986; Takeo, 1987; Beroza and Spudich, 1988; Hartzell, 1989; Das and Kostrov, 1990). The inversion methods differ, but the procedure is similar in that it requires a prior knowledge of the earthquake fault geometry.

One of these techniques is the linear method developed by Hartzell and Heaton (1983), which has been applied extensively to both teleseismic and near-source records of many large shallow interplate and intraplate earthquakes. Initial applications...

At 01:51 on 3 October 1995 (UT) a M_w 6.8 earthquake located at 2.80°S, 77.96°W at a depth of 16 km (Figure 1) occurred on the southeastern flank of Cutucu cordillera, a NNE-SSW Jurassic-Cretacic anticline, located on the western edge of the Subandean zone (Figure 1). This uplift overthrusts the Eastern flank of the Subandean zone along several reverse N-S faults.

No foreshock activity was detected before the main shock at the M_l 3.0 detection level of the National Ecuadorian Network run by the Instituto Geofísico of the Escuela Politécnica Nacional of Quito. Four large aftershocks (magnitude ≥ 5.1) were observed within the first 4 days after the main event, including a m_b 5.6 six minutes later and the M_w 6.4 main aftershock eleven hours later. Three other aftershocks with m_b 5.1 occurred in the period 21-29 October. About 750 aftershocks (M_l 3.0) were detected by the permanent network one...

INTRODUCTION

One of the regions with high seismicity in Mexico is the Oaxaca region, which is one that is most periodically affected by earthquakes that cause serious damage. This seismic activity is associated with the subduction process of the Cocos Plate under the North America Plate (NOAM). However, this region shows anomalous characteristics for a subduction zone, and this fact has prompted some researchers to consider this region as a truncated continental margin (e.g., Karig et al., 1978; Ortega-Gutiérrez, 1981; Bellon et al., 1982; McMillen et al., 1982; Nixon, 1982; Bevis and Isaks, 1984; Burbach et al., 1984; Schubert and Cebull, 1984).

In the Oaxaca region many studies such as microearthquake observation campaigns, aftershocks studies (for the 1978, 1980, 1982, and 1995 earthquakes), and refraction seismic studies among others have been carried out (e.g., Ponce et al., 1979; Núñez-Cornú et al., 1979; Singh et al., 1980; Chael and Stewart, 1982;...

INTRODUCTION

Earthquake prediction is still in its pre-feasibility stage. Empirical techniques based on the concept of seismic gaps (Fedotov, 1965; Sykes, 1968) are difficult to put in quantitative terms. The disagreement, before the destructive 1985 Mexico earthquake, on whether the Michoacán, Mexico gap had rupture potential is an example. Some seismologists actually argued that the gap was aseismic and incapable of generating major earthquakes. Such ambiguous interpretations of seismic gaps are not easily avoided in the present state of the art.

Yet most large earthquakes continue to occur in seismic gaps. This may or may not have something to do with the fact that many segments of plate boundaries, perhaps the majority, have been designated as seismic gaps by someone. On the other hand, the gaps assigned maximum seismic potential (e.g., by Nishenko and McCann, 1981) correlate rather poorly with the locations of major earthquakes.

The MRI algorithm (Lomnitz, 1993)...

At 6:52 pm PDT Wednesday, July 10, 1996, a large block of granite, with an estimated volume of 35,000 to 80,000 cubic yards (27,000 to 62,000 m³), detached from the cliff between Washburn Point and Glacier Point, in Yosemite Valley. The rock mass subsequently slid down a 50-degree inclined shelf on the cliff for approximately 185 m and acquired a velocity of 61 m/s (135 mph), sufficient to launch itself from the cliff. The rock then free-fell ballistically and cleared the remaining 500 m (1,640 feet) of the cliff prior to impacting on the talus slope, about 60 m (200 feet) from its base, in the Happy Isles area of the valley floor in Yosemite National Park. The rock fall was well recorded by 3 UC Berkeley (BDSN) and Caltech (TERRAscope) broadband seismographic stations and 15 short-period seismographic stations (operated by the USGS in Menlo Park and the University of...

SHORT NOTE

On January 11, 1996 an extremely unusual recording was made by the Geological Survey of Canada's seismograph network. We have identified the source, and, to our knowledge, this is the first recording of its type. The purpose of this short note is to document this extremely rare seismogram.

On January 11, 1996 at approximately 3:45 pm local time (23:45 UT), the emergent onset of a significant seismic event was noticed at the station ALB of the Western Canadian Telemetered Network (WCTN). This seismic station, operated by the Geological Survey of Canada, is located on central Vancouver Island, above the Cascadia subduction zone. It consists of a short-period vertical seismometer buried in a concrete vault, in a quiet wooded setting (Figure la). The instrumentation is not far from a local school on the outskirts of Port Alberni, British Columbia. The digital seismic signals are telemetered to the Pacific Geoscience Centre...

How often have we heard the term “realtime” applied to some sort of seismic analysis or process? “Realtime epicenter determination,” “realtime moment tensor solution,” and “realtime earthquake notification” are terms being routinely used to describe current seismic processing. Of course, this is usually a misapplication of the term “realtime.” According to Webster, realtime means “the actual time during which something takes place” and according to the Oxford English Dictionary, it means “the actual time during which a process or event occurs, especially, one analyzed by a computer.” In the strictest sense, for earthquake locations and mechanisms “realtime” would mean during the actual faulting process. A more liberal interpretation might be analysis during the arrival of seismic waves. Currently seismologists seem to use the term “realtime” to mean “automatic” or “pretty soon after.” A 1991 report of the National Research Council entitled “Realtime Earthquake Monitoring” included discussions of early warning and...

GSA TO HOLD PENROSE CONFERENCE

The Geological Society of America will hold a Penrose Conference “Tectonics of Continental Interiors” September 23-28, 1997 at Brian Head Resort near Cedar City, Utah.

Continental-interior regions account for over 80% of the surface area of continents today. In many of these regions, continental crust has not been metamorphosed to high grades, nor has it been penetratively transposed within a continental-margin setting since the Precambrian. As such, continental interiors include regions that have been shields or platforms for all or part of the Phanerozoic. The goal of this conference is to bring together a multidisciplinary group of geoscientists (structural geologists, geophysicists, geodynamicists, stratigraphers, and geochemists) to address the issue of how continental-interior regions worldwide formed and how they have behaved tectonically subsequent to their formation.

The conference will be organized around five major themes, ordered so that each new theme builds on the previous ones...

AGU Publishes Career Guide for Scientists

Finding the right job in today's market is difficult at best, but help is now available. To Boldly Go...A Practical Career Guide for Scientists by Dr. Peter Fiske is written specifically for scientists and graduate students in science who are having a difficult time applying their scientific training to the job market. To Boldly Go provides the tools necessary to compete in today's tough job market. Dr. Fiske discusses the changing role of the sciences and how one can apply specific scientific training to non-traditional careers. He emphasizes self-assessment and extensive research into the job market, but says that one need not dismiss the idea of an academic career. Dr. Fiske includes practical tips on writing resumes, CVs, and cover letters, as well as tips on interviewing techniques.

To order your copy of To Boldly Go please call 1-800-966-2481. The price for non-AGU members...

SEISMOLOGICAL SOCIETY OF AMERICA 92nd ANNUAL MEETING

April 9-11, 1997 (Wednesday-Friday) Hawaiian Regent Hotel, Honolulu, Hawai'i, USA

For Current Information: Via e-mail: ssa7@ginger.bachman.hawaii.edu Via WWW: http://www.soest.hawaii.edu/ssa97.html

92nd Annual Meeting of the Seismological Society of America Honolulu, Hawai'i April 9-11, 1997

Full payment must accompany registration

For multiple registrations, please duplicate this form

Dr. Ms. Mrs. Mr.

The 91st Annual Meeting of the Seismological Society of America was held April 1-3 in Cervantes Convention Center at the “America's Center,” St. Louis Missouri.

The Annual Business Meeting was held at a luncheon on April 2. Approximately 180 people attended. President Steven G. Wesnousky welcomed members to St. Louis and introduced the Head Table. He urged members to submit material to the new Seismological Research Letters.

Wesnousky reported on the Board of Directors meeting of March 31, 1996 and said that the fiscal health of the Society was good. He stated that there would be no increase in dues for the coming year and no increase in page charge fees. He introduced the expanded Board of Editors for BSSA. He thanked Ta-Liang Teng and Keiiti Aki for their work as co-editors of the dedicated BSSA issue on the Northridge earthquake of January 1994. He also thanked the National Science...

1996

December 6-8. SCEC-Sponsored Field Trip with Dr. Kerry Sieh.

Will inspect the southern San Andreas Fault system. Begin in San Bernadino and head south, ending up in Palm Springs. Southern California Earthquake Center, Los Angeles, CA, phone 213-740-1560.

December 6-11. First International Symposium on Earthquake Resistant Engineering Structures, Thessaloniki, Greece.

Sponsors: Aristotle University of Thessaloniki; Wessex Institute of Technology, others. S. Owen, ERES 1996 Conference Secretariat, Ashurst Lodge, Ashurst Southampton SO40 7AA, United Kingdom, phone 44-1703-293-223; fax 44-1703-292-853; e-mail wit@wessex.witcmi.as.uk

December 15-19. American Geophysical Union 1996 Fall Meeting, San Francisco, California.

Margot van Black, Meeting Manager, AGU; fax 202-328-0566; e-mail mvanblack@kosmos.agu.org

1997

January 30-February 1. Symposium in Honor of Vitelmo Bertero, Berkeley, CA.

Sponsors: University of California, Berkeley, Earthquake Engineering Research Center, California Universitites for Research in Earthquake Engineering. EERC-CUREe Bertero Symposium, EERC, 1301 S. 46th Street, Richmond CA 94804-4698, phone 510-231-9554; fax 510-210-9471; e-mail admin@eerc.berkeley.edu

February 3-5. Karlsruhe...