The 26 December 2004 Sumatara-Andaman (Mw 9.3) and the 8 October 2005 Kashmir earthquake (Mw 7.6) are two recent damaging earthquakes of South Asia that caused a huge damage to both property and person of most coastal countries southeast Asia including India and Pakistan. The 2004 Sumatra earthquake and the 2005 Kashmir earthquake are associated with two different subduction processes: for the Sumatra earthquake, the Indian plate is subducting beneath the Burma plate in the Indian Ocean, while for the Kashmir earthquake, the subduction of Indian plate occurs beneath the Eurasian plate in the Hiamalayan range. These two different subduction scenarios complicate the seismotectonics of the region. In order to better understand the earthquake generating processes of these two earthquakes a comprehensive study is made using a large amount of aftershock data from these two earthquakes.
A strong lateral heterogeneity is imaged beneath the Andaman-Nicobar region that shows a good correspondence to the local and regional tectonics. The subducting Indian plate and the volcanic zones in the Andaman-Nicobar region are found to be associated with high-V and low-V, respectively. The nature and extent of the imaged heterogeneity beneath the Andaman-Nicobar region demonstrate its strong bearing on genesis of aftershocks. A thorough analysis of the focal mechanism solutions of the 8 October 2005 Kashmir mainshock and its aftershocks revealed that there was sufficient amount of strain-partitioning in the vicinity of the Indo-Kohistan Seismic zone (IKSZ) where the 1974 Pattan earthquake (Mw 6.0) occurred. The Kashmir earthquake has indicated a N40?W trending 120×50 Km rupture area along the IKSZ where almost all earthquakes have strike towards NW-SE direction with fewer exceptions having nodal planes oriented approximately to E-W direction. The northeastern elevated hanging wall block of the IKSZ is calculated to be slipped up by about 1.5 - 1.9 meters, considering rock rigidity of 4×1011 - 3×1011 dynes/cm, suggesting the possibility of geometrical and inhomogeneous barriers and sharp and dull stress concentrations around the mainshock rupture zone. We suggest that the seismogenically active IKSZ was the principal source zone for the 1974 Pattan earthquakes and the 2005 Kashmir earthquakes, where the process of crustal exhumation and decollement of crustal layers might have facilitated the geneses of the 8 October 2005 Kashmir earthquake and its aftershock sequence.
If time permits, a detailed discussion on some of other research topics that carried out in seismological Laboratory of GRC during my stay would be discussed.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
