HR: 1330h
AN: S52F-0176    [PDF]
TI: Initiation Process of Moderate Earthquakes in the Northern Miyagi, Japan, Earthquake Sequence.
AU: * Sato, K
EM: sato@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Mori, J
EM: mori@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: Scaling relationships between the durations of the beginning portion of P-waves and final sizes of earthquakes have been reported by several studies (e.g. Iio [1992]). These studies mainly targeted microearthquakes and moderate to large earthquakes have been analyzed in only few studies. We tried to determine whether such scaling relationships hold for larger events, because it especially important for understanding the initiation processes of large earthquakes. We analyzed several moderate (magnitude up to 5) earthquakes and two large (magnitude 6 to 7) earthquakes and concluded that there may be a scaling relationship for small to moderate events but the scaling probably does not hold for the larger events. An earthquake sequence including several moderate earthquakes (magnitude up to 6.2) began on July 26, 2003 (JST) in the Northern Miyagi region, Japan. To study characteristics of initial phases of the moderate earthquakes, we analyze 4 $<$ M $<$ 6.2 events in the sequence. In this study, we employ the method which we used in the past study, a source model of Sato and Kanamori [1999]. The initial rupture of an earthquake is described with two parameters in this model: trigger factor and initial crack size. The trigger factor represents the contrast of surface energy on the edge of a crack and off of the crack. A large value for the trigger factor means that very high surface energy exists only on the edge and smaller surface energy off of the edge and rupture propagates spontaneously. A smaller value means that similar values of surface energy exists on and off of the edge and rupture propagates gradually depending on the initial crack size. We can use clearly recorded data from several near source borehole stations which are operated by Hi-net, NIED. We analyze 11 events with magnitude between 4.0 and 6.2. Hypocenter locations determined by the Japan Meteorological Agency and focal mechanisms determined by F-net, NIED are used. For these events, we obtain the results that all events can be explained by a small trigger factor and their initial crack sizes are between 15 and 50m. We can see a scaling relationship that the largest event (M6.2) has the largest initial crack size. However, we can also see that similarly sized events began from various initial cracks.
UR: http://www.rcep.dpri.kyoto-u.ac.jp/~sato/
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2003 Fall Meeting