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Through forward multiple-event analysis of teleseismic P-waves using source time functions (STFs), derived by non-negative time-domain deconvolution, we inferred the rupture features of the 2018 Hualien earthquake. At least six sub-events composed the Hualien earthquake, with the largest one (corresponding to Mw = 6.3) occurring 4.8 s later than the initiation of rupture. The total seismic moment (M0) of 6.48 × 1018 Nm (Mw = 6.5) and radiated seismic energy (ES) of 1.76 × 1014 Nm led to the ES/M0 ratio ~2.72 × 10-5. A static stress drop (ΔσS) of 5.03 MPa was also derived for the earthquake. On average, the rupture parameters of the 2018 Hualien earthquake from this study were similar to globally average values. From M0 and source duration (10.9 s), this implied an average rupture velocity (Vr) less than 2.0 km s-1. The forward multiple-event modeling showed that ΔσS varied with the sub-events and increased with ES/M0 to imply the frictional strength being heterogeneous along the fault. From the highest STF peak (6.9 s after the initiation) near the land-sea interface, we suggested that the Hualien earthquake be divided into two rupture processes. One with low ΔσS, low ES/M0, and high Vr occurred at sea; the other with high ΔσS, high ES/M0, and low Vr occurred on land. Both seawater and local velocity structures probably played crucial factors behind these rupture discrepancies during the 2018 Hualien earthquake.

A moderate-sized earthquake (ML = 6.4), named the 2010 JiaSian earthquake, occurred in southern Taiwan on March 4, 2010. Reports from several institutes indicated that the JiaSian earthquake had focal depths of 18–28 km and ruptures with a thrust mechanism. However, modeling of teleseismic P-waves in previously reported source parameters revealed significant differences between the observed and synthetic P-waves. Therefore, this study reexamined the source parameters of the 2010 JiaSian earthquake using a teleseismic P-wave inversion method. The inversion showed that the earthquake had a depth of 22 km, a best double couple of 304°/28°/48° and 170°/70°/110° (strike/dip/rake), and a seismic moment of 2.31 × 1018 N m (MW = 6.2). Rupture directivity analysis also suggested that the earthquake was a unilateral faulting event on the fault plane of 304°/28°/48°. The average source duration and the rupture length were ∼5.2 s and ∼19.4 km, respectively. The optimal rupture direction, measured counterclockwise from the strike on the fault plane, was 347°, which was projected onto the surface to correspond to the northwestward rupture, consistent with the aftershock distribution. The analysis also suggested a high rupture velocity during faulting, probably approximate to the crustal S-wave velocity, which may have resulted in a low static stress drop and caused the differences in PGA distribution along the direction of earthquake rupture. The dip angles of the fault plane estimated from the initial and centroid depths showed the initial rupture at a lower dip-angle plane and the later rupture at a higher dip-angle one.

The fault parameters of the 2008 Wenchuan earthquake were studied in a rupture directivity analysis by simultaneously inverting the period of the first Fourier spectral-node and the 100-s phase-delay time of the Rayleigh wave. The results show that the earthquake is a unilateral event with an optimal rupture azimuth of N59°E, consistent with the distribution of aftershocks. They also indicate that the fault plane strike is in the NE-SW direction, corresponding to the fault plane strike of 238° and NW-dipping (reported by the USGS). The inversion shows the source duration (including the rise time and rupture time) and rise time are 70±0.8 s and 9.3±0.6 s, respectively. The rupture velocity estimated only from the rupture time exhibits relatively higher value, 3.45±0.10 km/s, close to or larger than the S-wave velocity in the crust. One possible cause is that the rupture mechanism transferred from the thrust faulting in the southwestern portion of the fault to the strike-slip faulting in the northeastern one. The rise time offers an estimate of the dynamic stress drop (37.8±2.3 bars), from which through a macroscopic view the radiated seismic energy of (5.93±0.4) × 1016 N m is calculated. Although the estimated rupture length (∼210 km) and source duration are shorter than several source rupture models, the current analyses show the first-order rupture feature of the 2008 Wenchuan earthquake rupturing the Longmenshan fault zone.

We investigate the fault parameters of the 2005 Miyagi-Oki (Japan) earthquake using duration variations of teleseismic P-waves. The results show that the earthquake has a thrust-type mechanism and a seismic moment of 4.46 ¡_ 1019 Nm. Rupture directivity analysis suggests that the earthquake occurred as a result of a bilateral faulting on the fault plane with a strike of 247¢X, a dip of 17¢X and a slip of 125¢X. The optimal rupture azimuth, measured counterclockwise from the strike on the fault plane, is 170¢X (or 350¢X). The rupture length and average source duration are estimated to be 73.4 km and 14.5 sec, respectively. Thus the rupture velocity is 2.53 km sec-1 (~0.57 times the value of S-wave velocity), which is lower than the value for other similarly sized earthquakes. This implies that the 2005 Miyagi-Oki earthquake was probably a slow event. Consequently, there may have been less release of high-frequency seismic energy, leading to lower radiated seismic energy and radiation efficiency (~0.32 - 0.48). In other words, relatively larger fracture energy occurred during earthquake faulting in addition to the heat due to friction. The ratio of the static stress drop to the apparent stress (> 2.0) also suggests that the earthquake can be modeled as a frictional overshoot in a stress model, which implies the transformation of a lower percentage of strain energy into seismic-wave energy during the process of earthquake rupturing.

A concept of differential delay time is proposed for refraction static correction without picking first arrival times in the CDP reflection data processing. This new method is a modification of the ABCD method; it uses cross-correlation to measure the first arrival time difference between signals received at stations B and C, instead of directly computing them from their picked times. By taking advantage of multiple-fold CDP data, we apply the "line-up trace" measurement of cross-correlations, which may alleviate the effect of data imperfections. The problem of refractor velocity variation has also been solved to a certain extent, which allows for a reliable delay time to be adequately estimated for each station and consequently the static correction value. A synthetic model and a real case with a severe weathered layer problem have been tested to evaluate the method. Stable and man age able computation processes have been explored to attain the maximum performance. The results are quite satisfactory. It should be possible to apply this method in rough areas with complicated refraction static problem, even in 3D cases.

Short-period fundamental-mode Rayleigh waves with periods of 1.1∼5.5 sec were used to investigate the lateral variations of shallow-depth shear-wave velocity structure up to a depth of 8 km under southwestern Taiwan. Through a priori regionalization, the region was divided into three subregions from the west to the east, and then the regionalized group velocity for each subregion was determined by a standard least-squares technique. By the structure inversion, the study region had obviously lateral velocity variations, which systemically increased from the west region to the east one. On the whole, the shear-wave velocity in the Western Foothills was higher than that in the Western Coastal Plain. Additionally, the three subregions all had a shear-wave velocity of less than 3 km/sec with the lowest one in the Western Coastal Plain near the coast, related to the thick sediments. These results were rather consistent with the geological features. For depths larger than 4 km, the velocity-gradient varying with depth in the Western Foothills was lower than that in the Western Coastal Plain. This is likely to interpret the reason that the seismic waves cannot be easily trapped within the Western Foothills; thus the short-period surface waves are poorly developed in that region.