Exploring the Deeper Crustal Structure Beneath the Tatun Volcanic Area, Taiwan

Abstract

The Tatun Volcano Group (TVG) is adjacent to the Taipei Basin in northern Taiwan. Recent analysis from geological, geochemical and geophysical observations shows that the activity of the TVG associated with volcanism is still significant. Ash dating suggests that the last eruption might have taken place 6000 years ago. Although the last eruption was only a few thousand years ago, it is still a great challenge to confirm the existence of magma reservoirs beneath the study area. Common conversion point (CCP) stacking of receiver functions is an effective method for imaging crustal structures along linear profiles. Therefore, we selected three profiles within our study area for imaging lateral variations of crustal structures by CCP stacking. We also applied receiver function inversion to analyze the crustal structure beneath the Mt. Huangzuei region within the TVG, in order to verify the existence of a magma reservoir. The CCP images show that there are obvious differences in structure images for various back azimuth coverage, and these differences may be related to the effects of anisotropy within our study area. Therefore, the receiver function inversion process considers velocity and anisotropy models for analyzing the magmatism and crustal structure. The azimuthal dependence of receiver function waveforms for the seismic stations studied indicated that the Moho discontinuity lies at\u2009~\u200920–25 km depth. Low-velocity layers are observed at an average depth of\u2009~\u200915–25 km within our seismic network. The significant low S-wave velocity layers near the TVG region may be explained as a layered intrusion complex, which is mainly horizontally oriented molten sills. Therefore, we speculate that the magma reservoirs have a higher probability of existence in the deeper crust of Mt. Huangzuei.