Issues

INTRODUCTION

Seismologists have always striven to determine earthquake parameters as soon as possible after an earthquake occurs. Now there are several research groups that routinely “broadcast” their rapid determinations of earthquake location, focal mechanism, size, and depth. We report on our efforts to produce and “broadcast” source time functions of earthquakes.

The steady march of technical progress in seismology has provided first for the rapid determination of epicenter and magnitude (e.g., from the National Earthquake Information Center [NEIC] and various regional networks). Technical requirements for this effort are that several stations have their output telemetered to some location where the arrivals can be picked and that at least one of these stations be well-calibrated so that magnitude can be estimated. This technical level and service has been available for several decades. In some cases, this procedure has been completely automated with earthquake alarms issued with no human intervention. It is...

INTRODUCTION

The Reno-Carson City urban corridor is the second most populated region in Nevada and lies in one of the most seismically active parts of the state. This has prompted the development of an earthquake scenario (dePolo et at., 1996) to assist with earthquake preparedness and emergency response planning within the corridor's communities. As part of this effort, we have estimated probabilities of a potentially damaging earthquake affecting the scenario area (see Figure 1) over a 50-year time period. This paper briefly describes local historical earthquakes of magnitude ≥ 6 and compares their occurrence rates with b-value curve extrapolations from the instrumental time period and with preliminary estimates based on local fault activity rates.

HISTORICAL EARTHQUAKES

Thirteen earthquakes of magnitude 6 or greater have occurred in the scenario region since 1850 (see Figure 1 and Table 1). These events are briefly described in the Appendix. For many of the earlier...

INTRODUCTION

On Monday, October 9, 1995, at 9:36 am local time (3:36 pm GMT), an earthquake with an epicenter located at 19.25° N and 104.19° W, a surface-wave magnitude of Ms = 7.3 (USGS) and a moment magnitude Mw = 7.6 (USGS) struck the area near the town of Manzanillo, Colima, affecting the southwestern part of Jalisco and northern part of Colima, Mexico (Figure 1). In the epicentral region, along 80 km of coastal area, about 17,000 structures in different villages and cities either collapsed or were heavily damaged, affecting nearly 45,000 inhabitants. At least 48 people in the city of Manzanillo, Colima and 10 in the affected area of Jalisco were killed by this earthquake.

Damage caused by strong ground motion and the resultant tsunami and liquefaction were reported at several communities of Jalisco and Colima. Some of the most damaged were: Cihuatlán, Jaluco, Melaque, Barra de Navidad, La...

INTRODUCTION

There are few countries whose geography and history have been so affected by earthquake and volcanic activity as El Salvador, the smallest republic in Central America (Figure 1). The capital, San Salvador (Figure 2), has the unenviable claim of being the Latin American city most frequently damaged by earthquakes. Since 1700, San Salvador has been severely damaged by earthquakes on at least 14 occasions (Harlow et al., 1993). The last destructive earthquake to affect San Salvador occurred on 10 October 1986, causing about 1,500 deaths and extensive damage over much of the city, as well as an economic loss equivalent to 31% of El Salvador's GNP (Coburn and Spence, 1992).

El Salvador has been the focus of several studies of seismicity and seismic hazard, and the San Salvador earthquake of October 1986 generated renewed interest in the area. Three major hazard studies have produced seismic zonifications of El Salvador...

INTRODUCTION

The Collaborative Research Center (CRC) 461 Strong Earthquakes: A Challenge for Geosciences and Civil Engineering has been funded by the Deutsche Forschungsgemeinschaft (German Research Foundation) and is supported by the State of Baden-Würtemberg and the University of Karlsruhe. Collaborative Research Centers (SonderForschungsBereiche—SFB) aim at strategic research on issues that require intensive cooperation across various disciplines. CRCs form a framework for the development of these interactions and are expected to operate with a long-term (6 to 12 years) perspective. CRCs are peer-reviewed every three years. CRC 461 was established in July 1996 and aims at strategic research in the field of strong earthquakes with a regional focus on earthquakes and earthquake engineering in Romania.

OBJECTIVES

The focus of the research program is the strong earthquake activity in the Romanian Vrancea area (Figure 1). Over several centuries strong earthquakes in this area have caused a high toll of casualties and damage...

INTRODUCTION

In this time of federal budget cuts and program evaluations, a concern expressed by Congress is that socially important results of geologic and geophysical studies are not being disseminated to the public. With respect to earthquakes, the U.S. Geological Survey (USGS) has responded to this concern in the National Earthquake Hazards Reduction Program (NEHRP) by soliciting research proposals that focus on public education of earthquake hazards. This call by the USGS has prompted some new attempts to get information to the public. Individuals and emergency services organizations are active in a variety of earthquake hazard education programs. Of the various types of programs, we believe that a particularly effective means of earthquake education is achieved by the collaboration of an earth scientist with a specialist within a target population. In the example we document here, a nurse and a geologist collaborated in earthquake hazards education for registered nurses working...

COMPARISON OF RAYLEIGH-WAVE DISPERSION METHOD USING ARRAY MEASUREMENT OF MICROTREMORS AND DOWNHOLE LOGGING METHOD FOR DETERMINING SHEAR-WAVE VELOCITY PROFILES

LIU, H.-P., BOORE, D.M., JOYNER, W.B., OPPENHEIMER, D.H., WARRICK, R.E., ZHANG W.¹, and HAMILTON, J.C., U.S. Geological Survey, Menlo Park, CA 94025, [email protected]; ¹Permanent address: Beijing Strong-Motion Observation Center, State Seismological Bureau, Beijing 100080, CHINA

In earthquake engineering, site characterization is often done in terms of an average shear-wave velocity over a given depth. Shear-wave velocities are best determined using direct downhole and crosshole methods. However, for these methods, the drilling and cutting disposal costs are high. Indirect and non-intrusive methods of measuring shear-wave velocities by inversion of Rayleigh-wave dispersion curves offer the possibility of obtaining equivalent data at much lower cost. While some seismologists and geotechnical engineers use active sources for surface-wave generation, many shear-wave profiles have been determined in Japan by inverting Rayleigh-wave dispersion curves obtained from...