HR: 08:50h
AN: T11A-04    [PDF]
TI: Significant contributions from shallow sediments to PKP travel time delays and the implications: an example from Taiwan and its nearby islands
AU: * Huang, B
EM: hwbs@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, P.O.Box 1-55, Nankang, Taipei, 115 Taiwan
AU: Chen, K
EM:
AF: Institute of Earth Sciences, Academia Sinica, P.O.Box 1-55, Nankang, Taipei, 115 Taiwan
AU: Yen, H
EM:
AF: Institute of Geophysics, National Central University, Chung-Li, 000 Taiwan
AB: PKP waves, which penetrate the Earth's core and arrive back at the Earth­Ýs surface at near vertical incident angles, are generally regarded as invaluable when it comes to probing deep Earth structures. Such observations provide an ideal opportunity to measure individual travel time residuals and thereby independently examine either seismic velocity models from different approaches or regional tectonic models based on a variety of geodynamic hypotheses. However, the contribution of travel time delays from shallow geological structures to PKP travel time residuals is, however, quite general undefined in any seismic array, and accordingly, their implications have rarely been discussed. Relative PKP travel time residuals determined in the Taiwan region vary from -2.5 to +2.0 seconds, a range greater than the highest teleseismic travel time delays from deep earth. These data were used in this study to evaluate two three-dimensional crustal models of Taiwan derived from updated tomographic inversion studies. It is found that the tomographic models are able to predict PKP delay times of less than 40% and the PKP residuals are indeed consistent with the values of station corrections used in determining local earthquakes. Employing detailed gravity measurements, we interpreted these data to infer lateral heterogeneity beneath Taiwan. It is to be noted that the observed PKP residuals in Taiwan are strongly affected by the travel time delays of shallow sediments and that both of the 3-D regional crustal models failed to consider this low velocity layer. The implications of this study are that the time delays from shallow sediments obstruct the seismic inversion of deep earth structures when teleseismic waves are used and that local earthquake locations beneath thick sediments cannot, therefore, be accurately determined.
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting