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We investigate the temporal and spatial seismicity patterns prior to eight M > 6 events nucleating in different region of Taiwan through region-time-length algorithm and analysis of self-organizing spinodal model. Our results reveal that the spatiotemporial seismicity variations during the preparation process of impending earthquakes would display distinctive pattern corresponding to the tectonic setting. Q-type events occur in southern Taiwan and experience seismic quiescence stage prior to the mainshock. Seismicity decrease of 2.5 < M < 4.5 events around the high b-value southern Central Range, which contributes to accumulate the tectonic stress for preparing the occurrence of the Q-type event. On the other hand, A-type events occur in central Taiwan and experience seismic activation stage prior to the mainshock, which nucleated on the edge of the seismic activation area. We should pay attention when accelerating seismicity of 3 < M < 5 events appears within the low b-value area, which would promote the nucleation process of the A-type event. [ABSTRACT FROM AUTHOR]

The 2018 Mw 6.4 Hualien earthquake struck the eastern Taiwan and caused serious damage. We investigate the rupture properties of the 2018 Hualien earthquake by inverting teleseismic body wave and forward modeling GPS coseismic deformation. The rupture process and slip pattern of preferred model explain both the far-field (teleseismic data) and near-field (GPS) observations. The results show that the 2018 Hualien mainshock ruptured southward on two fault segments, with a weak but fast initiation (3.0 km s-1) in the main west-dipping segment F1 and slow (2.0 km s-1) yet significant slip on shallow east-dipping segment F2. In the past few years, several moderate-sized events, which struck eastern Taiwan and caused strong ground shaking and some seismic damage, are considered occurring on the west-dipping fault. Additional investigations are required to building up the knowledge of this not wellknown region. [ABSTRACT FROM AUTHOR]

The 2016 ML 6.6 Meinong earthquake struck southern Taiwan and caused serious damage due to the strong ground shaking. Anomalous seismicity spatiotemporal signature changes were identified prior to the 2016 Meinong event. We investigate the seismicity rate changes associated with the 2016 Meinong mainshock by applying the region-time-length (RTL) algorithm. The temporal result reveals a long obvious seismic quiescence stage soon after the 2012 Wutai event lasting until the 2016 Meinong mainshock. The spatial pattern of different background period lengths all exhibit that the 2016 Meinong event occurred near the abnormal seismic quiescence patch. Our study shows that the spatiotemporal information of the seismicity change could be a useful indication for potential seismic-hazard assessment. [ABSTRACT FROM AUTHOR]

The 2013 ML 6.4 Ruisui earthquake struck a seismic gap around the northern part of the Longitudinal Valley where rare earthquakes have occurred for at least two decades. Seismic data with different frequency bands connote a diverse scale of source characteristics. The slip model derived by a previous study using long-period seismic data provided us with the preliminary earthquake source properties in low-frequency energy radiation. However, the high-frequency part of the seismic energy needs to be considered for the strong motions in the comprehensive frequency band. As a case study, we carried out broadband strong motion simulations through the hybrid scheme, which simulated waveforms combining the low-frequency motions (frequency-wavenumber integration method) and high-frequency motions (empirical Green's function method) to reveal the strong ground motion and source characteristics of the 2013 Ruisui earthquake. The results show that even though the local structure is complicated this hybrid simulation can effectively rebuild the overall broadband strong ground motion characteristics for the 2013 Ruisui earthquake. Additional study issues are required to better understand the nature of localized high peak ground acceleration and the related seismic hazards for future earthquakes. [ABSTRACT FROM AUTHOR]

We investigated broadband evidence of the rupture directivity effect and estimated stress drop for the 2013 Nantou blind-thrust earthquakes (the 0327 and 0602 crustal events) from three individual analyses using empirical Green's functions: deconvolution source time function analysis, source spectral ratio analysis, and broadband waveform modeling of a strong-motion generation area. Although these two adjacent events have similar focal mechanisms, the 0327 event shows only up-dip directivity to the west, with an estimated stress drop of 9.0 MPa, and the 0602 event displays significant rupture directivity to the southwest, with an estimated stress drop of 14.2 MPa. The obvious variance in the rupture behavior and stress drop of these two nearby events, which might be related to immature blind faulting, suggests that this region requires additional study of the stress heterogeneity to better assess the seismic hazard. [ABSTRACT FROM AUTHOR]

From the end of August to early September 2011, 15 ocean-bottom seismometers (OBSs) were deployed offshore northeastern Taiwan for approximately 20 days. During this period, the typhoon Nanmadol formed in the western Pacific, moved northwestward from the East Philippines, and made landfall on the island of Taiwan. In this study, we analyzed the seismic signals from the OBSs and the marine metrological data to investigate the influence of the typhoon on submarine seismic records. Our results show that the signals induced by the typhoon occurred mainly at approximately 0.15-0.5 Hz frequency. The magnitude of these signals depends substantially on water depth. Some exceptions, most likely generated by site effects, were observed. Also, a positive correlation exists between the signals energy and the local wave height, which suggests that the microseisms were affected by the pressure changes produced by the local wave activity as the typhoon passed over the stations. However, when an OBS was outside the typhoon periphery, any wave energy variations could only be caused by the elastic wave formed around the typhoon area, the energy of which is transmitted through the ocean bottom to the stations. Thus, no local waves were excited by the strong winds, and only a relatively small amount of energy was recorded. [ABSTRACT FROM AUTHOR]

Teleseicmic vertical P waves of an earthquake doublet occurring on 26 December 2006 offshore southwestern Taiwan are analyzed to recover spatial slip distribution. Ground-displacement records for period 0.01 - 0.5 Hz are inverted using linear inversion for finite fault analysis. Waveform inversion results show that a dual segment fault of different strike is necessary for the first event to explain teleseismic waveforms. The trend in fault geometry, thus, inferred was coincidentally consistent with the bathymetry in the fault rupture area, suggesting the possible tectonic structure controlling fault propagation. Both earthquakes show larger slip in the asperities near the hypocenter and there are two main asperities of similar moments. The first event ruptured along a high angle eastern dipping plane while the second event ruptured along a low-angle western dipping fault plane. The spatial distribution of the Pingtung earthquake doublet shows a compensative and conjugate relationship, and the seismic moments of the earthquake doublet were 2.7 x 1026 and 1.8 x 1026 dyne-cm, respectively. The stress drops corresponding to the asperities of the two earthquakes have values of 3 to 4 bars, individually, similar to the values observed in other subduction zones. [ABSTRACT FROM AUTHOR]