Seismic Tomography off SW Taiwan: A Joint Inversion from OBS and Onshore Data of 2006 Pingtung Aftershocks

We characterize fault geometries for moderate and large earthquakes in and offshore southwest (SW) Taiwan. Stress orientation estimates suggest that the first shock of the Pingtung earthquake may be characterized by slab flexure. A region of predominately normal-faulting earthquakes is also defined. Using the maximum-likelihood Gutenberg-Richter relation, we find that the repeat times for magnitude, M 6.5 and M 7.0 earthquakes are approximately 30 and 80 years, respectively. By assuming a Gaussian probability distribution with a standard deviation of 0.4 the recurrence time, we estimate a 50% probability of an M 6.5 earthquake recurring in the next 30 years, while only a 20% probability of an M 7.0 in the next 50 years. To test the empirical relation that is currently being used to convert M L to seismic moment (M 0 ), we test the well-defined energy to moment ratio (E/M 0 ) for the region. We additionally utilize this method to identify the lack of slow-source earthquakes in several recent offshore events in Taiwan.

Section: Discussionmentioning

confidence: 72%

Earthquake Probabilities and Energy Characteristics of Seismicity Offshore Southwest Taiwan

Chen¹,

Newman

Wu³

et al. 2008

“…On 26 December 2006, at 20:26 and 20:34 (local time), two almost simultaneous double-event earthquakes of the same magnitude 7.0, only kilometers apart in distance and 8 minutes apart in time, occurred off southwest Taiwan (Pingtung earthquakes marked by EQ1 and EQ2 in Fig. 1) (Liao et al 2008). Shortly after the Pingtung earthquakes, local fishermen working in that area reported disturbed waters.…”

Section: Introductionmentioning

confidence: 99%

Turbidity Currents, Submarine Landslides and the 2006 Pingtung Earthquake off SW Taiwan

Hsu¹,

Kuo²,

Lo³

et al. 2008

Self Cite

212

107

Submarine landslides or slumps may generate turbidity currents consisting of mixture of sediment and water. Large and fast-moving turbidity currents can incise and erode continental margins and cause damage to artificial structures such as telecommunication cables on the seafloor. In this study, we report that eleven submarine cables across the Kaoping canyon and Manila trench were broken in sequence from 1500 to 4000 m deep, as a consequence of submarine landslides and turbidity currents associated with the 2006 Pingtung earthquakes offshore SW Taiwan. We have established a full-scale scenario and calculation of the turbidity currents along the Kaoping canyon channel from the middle continental slope to the adjacent deep ocean. Our results show that turbidity current velocities vary downstream ranging from 20 to 3.7 and 5.7 m s -1 , which demonstrates a positive relationship between turbidity current velocity and bathymetric slope. The violent cable failures happened in this case evidenced the destructive power of the turbidity current to seafloor or underwater facilities that should not be underestimated.

“…Most of these sediments bypass the upper and middle reaches of the canyon and are deposited in the lower canyon reach or in the Manila Trench (Yu et al 2009). One consequence is that the submarine telecommunication cables across the Kaoping submarine canyon were frequently broken due to turbidity currents along the channel (Hsu et al 2008;Su et al 2012). Morphologically, the middle Kaoping submarine canyon reach has incised the base of the continental slope and formed a deep V-shaped channel (Fig.…”

Section: Clusters Of Intensifying Seabed Gas Flow and Emissionmentioning

confidence: 99%

“…The submarine channel erosion along a bathymetric contour line could provide an effective steep slope for the BSR curve to increase the upward fluid flow rate and intensify submarine mud volcanism and gas seepage. The middle reach of the Kaoping Canyon could be associated with a thrust fault dipping northeastward (Liao et al 2008;Lin et al 2009) and may allow more free gas (mainly methane) at deep depths to migrate upward (Lin et al 2009;Chuang et al 2010). Compared to the other areas off SW Taiwan, the distance from the seafloor to the BSR is dramatically longer to the SW of the middle Kaoping Canyon reach (Fig.…”

Section: Clusters Of Intensifying Seabed Gas Flow and Emissionmentioning

confidence: 99%

Seabed gas emissions and submarine landslides off SW Taiwan

Hsu¹,

Lin

Wang³

et al. 2018

Self Cite

Methane emissions out of the seabed could seriously affect Earth's climate and are usually associated with the dissociation of gas hydrates stored in marine sediments on the continental margins. Spatially, gas emissions out of the seafloor are not evenly distributed in continental margins. Gas emissions out of the seabed generally occur through submarine mud volcanoes and gas seeps. To understand the seabed gas emissions off SW Taiwan, we investigate the distributions of active submarine mud volcanoes, gas seeps, and gas plumes off SW Taiwan. We examine all of the available sub-bottom profiler and EK echo sounder data. We identified 19 submarine mud volcanoes, 220 gas seeps, and 295 gas plumes. The gas emissions are generally distributed at the crests of mud diapiric ridges. Most of the active mud volcanoes and gas seeps cluster at the KASMVG (Kaoping submarine mud volcanoes group) area. We speculate that the intensive mud volcanism and gas seepage at the KASMVG area are ascribed to submarine channel erosion along the continental slope base. The erosion causes a deep V-shaped channel and a steep BSR (Bottom-Simulating Reflector) slope curve across the continental margin. The upward migration rate of free gas beneath the BSR is thus increased and intensifies mud volcanism and gas seepage at the KASMVG area. The gas seeps can reduce the slope stability and generate small-scale slides. The development of mud volcanoes in an area could effectively disturb the seabed morphology so that large-scale submarine landslides cannot easily happen.