<p>&#160; &#160; An ongoing triggered slow slip event (SSE) on the inland Hengchun fault after the 2006 <em>M<sub>L</sub></em> 7.0 Pingtung offshore earthquake in Taiwan is proposed in this study by analyzing the coordinate time series of 13 continuous GNSS stations, 37 campaign-mode GNSS stations and 3 precise leveling routes in Hengchun Peninsula from 2002 to 2022. Four surface velocity patterns have been determined based on these geodetic data: (1) the interseismic period from 2002 to the 2006 Pingtung offshore earthquake; (2) the 2<sup>nd</sup> period after the earthquake to April 2010; (3) the 3<sup>rd</sup> period from April 2010 to 2016; (4) the 4<sup>th</sup> period from 2016 till 2022. In general, a velocity discontinuity is discovered approximately located at 1-2 km east of the currently known Hengchun fault trace. Then we evaluate the slip deficit rate and slip rate distributions of the Hengchun fault through baseline inversion model and coseismic fault model, respectively. The modeling results shows that Hengchun fault is a reverse fault with a minor left-lateral component. Two asperities are shown in the southern and northern segments, respectively. Furthermore, the energy on the asperities has been gradually released from south to north after the 2006 earthquake, even though the postseismic deformation has faded. On the other hand, the geological investigation results also indicate that surface ruptures were generated on the Hengchun fault until 2017. Therefore, we infer that (1) the temporal pattern changes of surface velocity in Hengchun Peninsula are driven by the 2006 <em>M<sub>L</sub></em> 7.0 Pingtung offshore earthquake; (2) the Hengchun fault ought to be relocated at 1-2 km to the east; (3) a SSE occurs on the Hengchun fault after the 2006 <em>M<sub>L</sub></em> 7.0 Pingtung offshore earthquake. (4) the energy keeps releasing through the SSE after the earthquake and decrease the earthquake potential in Hengchun Peninsula.</p>
<p>A unified geodetic data-based earthquake catalog may provide the asperity information to improve the seismic hazard assessment. Therefore, we propose a unified geodetic data-based earthquake catalog in Taiwan from 2006-2018 using the geodetic data from 333 campaign-mode GNSS stations and 19 precise leveling routes and the published continuous GNSS data to improve the spatial resolution and reliability of vertical component in coseismic displacement fields. The coordinate time series analysis was used to derive the coseismic displacements of each earthquake from the sGNSS and precise leveling data by using the least square method. This earthquake catalog involves 2006 M<sub>L</sub> 7.0 Pingtung offshore earthquake, 2010 M<sub>L</sub> 6.4 Jiashian earthquake, March 2013 M<sub>L</sub> 6.2 Nantou earthquake, June 2013 M<sub>L</sub> 6.5 Nantou earthquake, 2013 M<sub>L</sub> 6.4 Ruisui earthquake, 2016 M<sub>L</sub> 6.6 Meinong earthquake, and 2018 M<sub>L</sub> 6.2 Hualien earthquake. Then the coseismic source models of these events were evaluated by inverting the coseismic displacement fields. Based on this earthquake catalog, we provided high spatial resolution and precision in the vertical deformation and the resolution of the modeled fault dip angle is also improved. In addition, unknown coseismically reactivated anticlinal structures in SW Taiwan were discovered in this study, which may be associated with the active mud diapirs. Finally, because of abundant coseismic geodetic data adopted in this study, the spatial resolution of coseismic slip distribution is also increased in those earthquake events.</p>
<p>While intraslab events in subducting oceanic slabs have been widely studied, intraslab earthquakes in slabs of continent-oceanic transition zones, where lithospheric rheology differs, remain little understood. Here, we investigate the 2006 Pingtung (southwestern Taiwan) offshore intraslab earthquake doublet (Mw 7.0 and Mw 6.9), striking around the northern Manila subduction zone, where the highly thinned continental crust subducts. The two main shocks were at the depth of ~40 &#8211; 60 km, below the local MOHO, and ~8 minutes apart. The several source models that have been proposed vary, and do not consider all available observations. In this study, we incorporate comprehensive datasets, including teleseismic body waves, regional broadband, near-field strong motion waveforms, and high-rate GNSS, to propose a new source model, and further discuss source characteristics in the regional tectonic context. We first determine a reliable near-field velocity model and the frequency ranges for waveform inversions by path calibration based on inverting a nearby Mw 5.6 aftershock. We then constrain the multiple point sources (MPS) solutions for both events. The location and fault planes from MPS are used to resolve slip distributions by finite fault inversions. We finally validate this slip model by the static coseismic displacement observed by the dense, near-field campaign GNSS and precise leveling. Our results show that the Mw 7.0 normal event ruptured a west-dipping fault at the depth of ~40 km, characterized by at least two major asperities. This rupture was followed by the deeper Mw 6.9 strike-slip event, located ~40 km to the north. The earthquake sequence was located around a failed rift indicated by seismic tomography and likely represented a reactivation of the faults formed in the mantle lithosphere during the continental rifting in the northern South China Sea margin. The doublet&#8217;s complex mechanisms could be explained by stress fields imposed by the subducting transitional crust.</p>
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