Local magnitude determined from a simulated Wood-Anderson seismograph

Abstract

The design of a seismograph to simulate the output of a Wood-Anderson seismograph is reported. Results demonstrate that the seismograph can satisfactorily simulate the Wood-Anderson seismograph at least in the frequency range from 1 to 10 Hz. The relationships between local magnitude ( M l ), body-wave magnitude ( m b ), seismic moment ( M o ), and duration magnitude ( M d ) for Taiwan earthquakes are: M l = (−0.604 ± 0.485) + (1.268 ± 0.094)m b , log M o = (14.571 ± 1.683) + (1.598 ± 0.236) M L and: M d = (0.187 ± 0.373) + (0.862 ± 0.066)M L The first two relationships are different from those for southern California earthquakes. For the same m b or M o , the local magnitude value of a Taiwan earthquake is larger than that of a southern Californian one. Thick sediments just below the simulated Wood-Anderson seismograph site probably amplify the short-period seismic waves, thus yielding larger local magnitude values for Taiwanese earthquakes. The different source properties in the two regions are also considered to contribute to the differences.