Abstract
This paper describes a new method for calculating strong motion records for a given seismic region on the basis of the laws of physics using information on the tectonics and physical properties of the earthquake fault. Our method is based on a earthquake model, called a «barrier model», which is characterized by five source parameters: fault length, width, maximum slip, rupture velocity, and barrier interval. The first three parameters may be constrained from plate tectonics, and the fourth parameter is roughly a constant. The most important parameter controlling the earthquake strong motion is the last parameter, «barrier interval». There are three methods to estimate the barrier interval for a given seismic region: 1) surface measurement of slip across fault breaks, 2) model fitting with observed near and far-field seismograms, and 3) scaling law data for small earthquakes in the region. The barrier intervals were estimated for a dozen earthquakes and four seismic regions by the above three methods. Our preliminary results for California suggest that the barrier interval may be determined if the maximum slip is given. The relation between the barrier interval and maximum slip varies from one seismic region to another. For example, the interval appears to be unusually long for Kilauea, Hawaii, which may explain why only scattered evidence of strong ground shaking was observed in the epicentral area of the Island of Hawaii earthquake of November 29, 1975. The stress drop associated with an individual fault segment estimated from the barrier interval and maximum slip lies between 100 and 1000 bars. These values are about one order of magnitude greater than those estimated earlier by the use of crack models without barriers. Thus, the barrier model can resolve, at least partially, the well known discrepancy between the stress-drops measured in the laboratory and those estimated for earthquakes.
Highlights
We are interested in predicting earthquake strong motion on the basis of the laws of physics using information on the tectonics and physical properties of the earthquake fault which can be measured at the present time
The earthquake model used by them was a propagating dislocation parametrized by fault length, fault width, rupture velocity, final uniform slip, and rise time
The new model allows us to estimate the barrier interval from the observed seismogram of an eartihquake, from the scaling law of seismic spectrum for small earthquakes in a seismic zone, and from the direct measurement of fault breaks along an earthquake fault
Summary
We are interested in predicting earthquake strong motion on the basis of the laws of physics using information on the tectonics and physical properties of the earthquake fault which can be measured at the present time. The earthquake model used by them was a propagating dislocation parametrized by fault length, fault width, rupture velocity, final uniform slip, and rise time Among these five parameters, the first four can be determined relatively from various seismological data and their reliable estimates have been obtained for many earhquakes. Because of difficulties in separating source and path effects on short period waves, the determination of this parameter has been made for only a few earthquakes To resolve this problem, we have taken two approaches: spectral analysis of small earthquakes and theoretical work on rupture propagation. The new model allows us to estimate the barrier interval from the observed seismogram of an eartihquake, from the scaling law of seismic spectrum for small earthquakes in a seismic zone, and from the direct measurement of fault breaks along an earthquake fault. The results will be summarized in a diagram showing barrier interval as a function of maximum slip
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