Modern Seismic Observations in the Tatun Volcano Region of Northern Taiwan: Seismic/Volcanic Hazard Adjacent to the Taipei Metropolitan Area

Abstract

ABSTRACT1 Institute of Geophysics, National Central University, Chung-Li, Taiwan, ROC The Tatun volcano group is located adjacent to the Taipei metropolitan area in northern Taiwan and was a result of episodic volcanisms between 2.8 and 0.2 Ma. Earthquake data collected over the last 30 years are analyzed to explore seismicity patterns and their associated mechanisms of faulting in the area. Using a Joint Hypocenter Determination (JHD) method, a few sequences of relocated earthquake hypocenters are tightly clustered; these seemed to be blurry in the original catalog locations. Numerous earthquakes, previously unnoticed and not reported in the CWB catalog, have been identified from careful examination of the continuous recordings of a nearby broadband seismic station. These newly identified earthquakes show similarities in waveforms and arrival time differences between direct P-and S-waves indicating that their hypocenter locations are very close to each other and their source mechanisms are similar. A relatively high b-value of 1.22 is obtained from the analysis of crustal earthquakes (depth < 30 km) in the region, which may suggest that clustered local seismicity in the Tatun volcanic region probably resulted from subsurface hydrothermal or volcano-related activities. Focal mechanism solutions determined in this study are dominated by normal faulting. Thus, these earthquake clusters are most probably associated with hydrothermal/magmatic activities in a back-arc extensional environment. TAO, Vol. 16, No. 3, August 2005 580

The Volcanic Earthquake Swarm of October 20, 2009 in the Tatun Area of Northern Taiwan

“…4). Although a few of the seismic swarms might have also taken place in some faults with aseismic slips, this is a seismic swarm that typically occurs in volcanic or geothermal areas (Kim et al 2005;Lin et al 2005a, b;Konstantinou et al 2007). On the other hand, the micro-earthquakes in the fault zone are often triggered by the main-shock and the number of triggered aftershocks then decays significantly over time (Lin 2004).…”

Deposits, character and timing of recent eruptions and gravitational collapses in Tatun Volcanic Group, Northern Taiwan: Hazard-related issues

“…Although the group has not had any historical eruptions, its volcanic edifices are well-preserved and are dotted by multiple hot springs and solfataras with temperatures up to 116°C (Witt et al, 2008). Detailed investigations undertaken in recent years have provided several lines of evidence that an active magma chamber is present below the TVG: (1) compositions of gases from the TVG fumaroles indicate their origin from a magmatic source (Yang et al, 1999;Lee et al, 2005;Lee et al, 2008;Witt et al, 2008); (2) shallow-level seismicity similar to seismicity under active volcanoes has recently been observed (Lin et al, 2005;Kim et al, 2005;Konstantinou et al, 2007); and (3) geodetic measurements (leveling and GPS) reveal steady local ground deformations of the TVG, which may be caused by pressure changes at depth, possibly associated with migration of magma and/or hydrothermal fluids (Yu et al, 1997;Konstantinou et al, 2007).…”

“…Subsidence can be more easily linked to purely tectonic reasons (for example to a graben associated with the formation of a pull-apart structure along a major strike-slip fault). Taipei Basin, which is located immediately to the south, experienced similar subsidence without involvement of volcanism (Kim et al, 2005).…”

“…1). In this region, two volcanic island arcs, Ryukyu and Luzon, merge (South China Sea and Philippine Sea plates are subducting in almost opposite directions) and simultaneously collide with the Eurasian continent (Kim et al, 2005;Hsu et al, 2009). However, the northern part of the Luzon arc has already been subducted (and partly obducted) under Eurasia and does not play a role in the recent volcanism of the TVG.…”

“…Song et al (2000a) provided a brief description of pyroclastic deposits and suggested a general scheme for the geological history of the group. More recently, the first volcanic hazard assessment for the TVG was provided (Kim et al, 2005).…”