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

[1] The geometrical structure of the responsible faults of the 20 September 1999 Chi-Chi, Taiwan, earthquake (M L = 7.3, M w = 7.6) and its aftershocks can be clearly depicted by well-located hypocenters and focal mechanisms of large aftershocks. The mainshock and two large aftershocks with M L = 6.8 were characterized by thrust faulting along a N-S striking fault plane dipping to the east. The underground structure of the Chelungpu fault, which is probably merging with the decollement beneath the Western Foothills, can be clearly associated with the seismicity pattern and the focal mechanisms of the three largest events. A group of deeper aftershocks including two moderate events (M L = 6.3 and 6.0, respectively) were located to the southeast of the mainshock along a fault plane dipping steeply to the west down to a depth of about 30 km. Our results suggest that the spatial pattern of the aftershocks in the southern part of the source area can be interpreted by a conjugate-fault system. This conjugate-fault system is comprised of the gently east-dipping Chelungpu fault and a steeply west-dipping deeper fault zone.

The source location of the 16 September 1994 Taiwan Strait earth quake was relocated based on the beam-forming method using joint seis mic observations from regional seismic networks in Taiwan and Fujian and the International Seismological Center Bulletin. The revised epicenter is located at latitude 22.37° N (±0.03°) and longitude 118.63° E (±0.03°). Re sults of this study showed that the location uncertainty has been signifi cantly reduced using this approach. Decomposition tests of this study showed that the epicenters of Taiwan Strait events can be determined by the beam forming method using data from densely distributed seismic stations in Tai wan. However, source depths of Taiwan Strait events can not be deter mined unambiguously using the first P-arrivals only. Seismic waveform data should be carefully re-examined using this method to investigate earth quake source properties and seismicity of the Taiwan Strait region.

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We study real-time correlators for N = 4 super Yang Mill fields coupled to a pair of entangled quarks beyond the probe limit using holography. Energy quanta sent from one quark perturb the quantum state of the fields and affect the other quark. We make the connection with the ER=EPR conjecture by considering the situation when two quarks are uniformly accelerating opposite to each other. The dynamics of quarks, in the gravity dual, is described by the string worldsheet theory, which in this case has the induced metric describing a two-sided AdS black hole, or a wormhole.Energy quanta sent by one of the quarks produce the shock wave on the worldsheet. We find the effect of shock wave on the boundary field correlators and we discuss the consequence for the ER=EPR conjecture.