Locating earthquakes with amplitude: Application to real-time seismology

Abstract

Earthquakes are traditionally located using travel times. However, since the ground-motion amplitude generally decays with the distance from the source, it should also be possible to locate earthquakes using amplitude data. Amplitudes are affected by many factors other than the distance, so that we do not expect to be able to locate the epicenter, the location of the initial rupture, very accurately with amplitude data. However, locating earthquakes with amplitudes has its own merits: (1) For postearthquake emergency services, it is often more important to know the spatial distribution of strong-motion parameters such as peak acceleration and peak velocity than the rupture initiation point itself (National Research Council, 1991). This is especially true for thrust earthquakes (e.g., 1971 San Fernando earthquake; 1987 Whittier Narrows earthquake) or events with large rupture zones. (2) The amplitudes are usually much easier to determine than the arrival times, especially for events with complex rupture patterns or with immediate foreshocks in which event association can be difficult. For application to real-time earthquake information systems such as CUBE (Caltech/USGS Broadcast of Earthquakes; Kanamori et al., 1991), the amplitude method could provide a quick and robust way to send useful information for emergency operations. Here, we report a few examples and propose a method for future implementation in a CUBE-type system.

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