Relocation of Early and Late Aftershocks of the 2001 Bhuj Earthquake Using Joint Hypocentral Determination (JHD) Technique: Implication toward the Continued Aftershock Activity for more than Four Years |
| |
Authors: | Prantik Mandal R Narsaiah B Sairam C Satyamurty I P Raju |
| |
Institution: | (1) National Geophysical Research Institute, Uppal Road, Hyderabad, 500007, India |
| |
Abstract: | We employed layered model joint hypocentral determination (JHD) with station corrections to improve location identification
for the 26 January, 2001 Mw 7.7 Bhuj early and late aftershock sequence. We relocated 999 early aftershocks using the data from a close combined network
(National Geophysical Research Institute, India and Center for Earthquake Research Institute, USA) of 8–18 digital seismographs
during 12–28 February, 2001. Additionally, 350 late aftershocks were also relocated using the data from 4–10 digital seismographs/accelerographs
during August 2002 to December 2004. These precisely relocated aftershocks (error in the epicentral location<30 meter, error
in the focal depth estimation < 50 meter) delineate an east-west trending blind thrust (North Wagad Fault, NWF) dipping (~
45°) southward, about 25 km north of Kachchh main land fault (KMF), as the causative fault for the 2001 Bhuj earthquake. The
aftershock zone is confined to a 60-km long and 40-km wide region lying between the KMF to the south and NWF to the north,
extending from 2 to 45 km depth. Estimated focal depths suggest that the aftershock zone became deeper with the passage of
time. The P- and S-wave station corrections determined from the JHD technique indicate that the larger values (both +ve and
-ve) characterize the central aftershock zone, which is surrounded by the zones of smaller values. The station corrections
vary from −0.9 to +1.1 sec for the P waves and from −0.7 to +1.4 sec for the S waves. The b-value and p-value of the whole
aftershock (2001–2004) sequences of Mw ≥ 3 are estimated to be 0.77 ± 0.02 and 0.99 ± 0.02, respectively. The p-value indicates a smaller value than the global
median of 1.1, suggesting a relatively slow decay of aftershocks, whereas, the relatively lower b-value (less than the average
b-value of 1.0 for stable continental region earthquakes of India) suggests a relatively higher probability for larger earthquakes
in Kachchh in comparison to other stable continental regions of the Indian Peninsula. Further, based on the b-value, mainshock
magnitude and maximum aftershock magnitude, the Bhuj aftershock sequence is categorized as the Mogi's type II sequence, indicating
the region to be of intermediate level of stresses and heterogeneous rocks. It is inferred that the decrease in p-value and
increase in aftershock zone, both spatially as well as depth over the passage of time, suggests that the decay of aftershocks
perhaps could be controlled by visco-elastic creep in the lower crust. |
| |
Keywords: | Joint Hypocentral Determination aftershocks b-value p-value station corrections |
本文献已被 SpringerLink 等数据库收录! |
|