Initial Investigation of the May 24, 1994 Hualien and June 5,1994 Nanao Earthquakes

 

Abstract

We investigate the characteristics of the May 24, 1994 Hualien and June 5, 1994 Nanao earthquakes using the long period P-wave data recorded by the IRIS (Incorporated Research Institution r Seismology). The solution based on long period P waves gives a mechanism with dip=23.6°, rake=-31.4° and strike=135.3°, and a seismic moment of 9.0x1025 1.3x1026 dyne-cm (Mw=6.6~6.7) for the Hualien earthquake; and with dip=62.6°, rake=25.0° and strike=293.2°, and a seismic moment of 3.73x1025dyne-cm (Mw=6.4) for the Nanao earthquake. The source time-function of the May 24, 1994 Hualien earthquake consisted of a main event with a time duration of 8 sec followed by two small subevents extending the total duration of the source time-function to 35 sec. This long duration of source ·time function and the difference between Ms and mb suggest the Hualien earthquake was a slow earthquake. The source time function of the June 5, 1994 Nanao earthquake had a time duration of 6 sec and was rather simple compared with Hualien earthquake. The average slips on the fault for the Hualien and Nanao earthquakes were 40~92.3 cm and 51.8 cm, respectively. The stress drops of the two intra-plate events were comparable to those of most large earthquake.

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