[1] The repetition of slip during rupture process of earthquake is a debate issue which had never been confirmed clearly in the past big events due to the lack of dense nearfield observations and limited resolution in time of source model. The 2011 M9.0 Tohoku-Oki earthquake generated a wealth seismic records which provided us an unprecedented opportunity to study the rupture evolution of giant earthquake at a high spatio-temporal resolution. Here we use teleseismic, local strong motion and near-field coseismic geodetic data to investigate the source rupture process of this event based on the parallel inversion technique. The results reveal a broad slip zone with remarkable large scale repeating slip during the earthquake. The inverted source model shows several time periods of energy release with three main peaks. These energy bursts and temporal rupture snapshots suggest repetition of a large scale slip on the biggest asperity. This rupture behavior resulted in >50 m slips on the slip zone and prolonged the entire rupture process for a long duration of ∼160 seconds. The proposed source model is in a good agreement with the aftershock distribution and can interpret the characteristics of local strong motions. Further investigations of repeating slip during this event are crucial which will deeply transform earthquake science from dynamic point of view. Citation: Lee,

Taiwan is located in a complex, tectonically active region where the Philippine Sea. plate is subducting northwestward along the Ryukyu Trench while the Eurasian plate is subducting eastward along the Manila Trench. The Central Weather Bureau Seismographic Network (CWBSN), which is composed of 75 stations with three-component instruments, has been operated over the island of Taiwan since March of 1991. This dense seismic network provides high-quality P-and S-wave arrival times of local earthquakes, and, thus, gives us a good opportunity to determine the velocity structure of the crust and upper mantle structures beneath Taiwan. We have applied a new tomographic method to infer the fine 3-D P-and S-wave velocity structures beneath Taiwan. Results show the existence of a low velocity zone in the uppercrust of west Taiwan. This zone is consistent with the thick sediments in the area. A low-velocity zone has been inferred underneath the extinct volcano regions, and it is due to the remnant geothermal effect after past volcanic activities. A low-velocity zone with a relatively homogeneous distribution of P-wave velocities, extending to a depth of about 30-35 km, is found beneath the Central Range. We infer that this feature might have resulted from the heat intrusion from the oceanic upper mantle of the Philippine Sea plate, which has been colliding with the Eurasian plate, and the effect of partial melting. The thickness of the crust of Taiwan is estimated to be 30-35 km and that for the Philippine Sea plate is 15-20 km.

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The ground-velocity recordings of the 20 September 1999, Chi-Chi, Taiwan earthquake recorded at stations near the ruptured fault trace show a simple, large-amplitude, and long-period pulse following the S wave, which is closely associated with the surface faulting and the rupture process of thrust faulting. The conspicuous pulse on the ground-velocity seismogram following the S-wave arrival, called the S 1 phase, is interpreted as the superposition of the rupture pulses that nucleate at an asperity near and underneath the station and propagate up-dip and laterally along the fault plane toward the surface stations. The arrival times of the S 1 phase and the onsets of the permanent displacement at stations near and along the ruptured fault trace increase with hypocentral distance, suggesting that the rupture of the Chi-Chi earthquake might have initiated at the hypocenter of the mainshock and propagated both upward and laterally from south to north. On the basis of the travel-time differences between the S 1 phase and the direct S wave at the stations near and along the ruptured fault trace, the rupture velocities varied from 2.28 to 2.69 km/sec, with an average rupture velocity of about 2.49 km/sec. The rupture velocities decreased from south to north.

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Scaling relations among seismic moment, M0, average displacement, δ, rupture width, W, and rupture length, L, of earthquake faults are studied mainly using the data base of earthquake source parameters compiled by Wells and Coppersmith (1994). Results show that seismic moment scales with rupture length approximately as M0 ∼ L2; rupture width is independent of rupture length for large earthquakes; average displacement relates to rupture length approximately as δ ∼ L; and the average displacement is independent of rupture width. Consequently, the L-model proposed by Scholz (1982) is more appropriate than the W-model suggested by Romanowicz (1992) to describe the scaling of earthquake faults.