Are the 7 March 2006 Mw 5.6 event and the 3 February 2006 Mw 4.58 event triggered by the five years continued occurrence of aftershocks of the 2001 Mw 7.7 Bhuj event?

摘要

We present the locations, ft-values and aftershock decay parameters for the aftershock sequences of the 2001 Mw 7.7 Bhuj and the 2006 Mw 5.6 GEDI events. A study of temporal distributions (2001-06) of earthquakes along the North Wagad Fault (NWF), Island Belt Fault (IBF) and GEDI Fault (GF) enabled us to infer that the 3 February 2006 event along IBF at 28.7 km depth and the 7 March 2006 event along GF at 2.2 km depth were triggered by the five years continued aftershock activity subsequent to the 2001 event. Analysis of focal mechanisms suggests dominance of reverse movements on the south-dipping NWF and IBF, but strike-slip motion is observed along GF. The 7 March event gives a large stress drop of 26.7 MPa, whereas those on 17 and 19 February 2006 suggest smaller stress drop values of the order of 1.5 MPa. However, the 3 February event is associated with an anomalously large stress drop of 70.6 MPa. The ft-value for the M > 3 Bhuj aftershock sequence (2001-05) is 0.77, but for the 2006 sequenceit is 0.81. It is inferred based on these low b-values that both the aftershock sequences could be categorized as the MOGI's type-II sequences, indicating a region of intermediate-level stresses and heterogeneous rocks. The p-value or aftershock decay exponent is estimated to be 0.99 and 0.88 for the 2001-05 and the 2006 sequence respectively. This is less than the global median of 1.1, suggesting slower decay for these two studied aftershock sequences.