Aftershocks of 26th january 2001 Bhuj earthquake and seismotectonics of the Kutch region

Abstract

The 26th January 2001 Bhuj earthquake was followed by intense aftershock activity. Aftershock data from United States Geological Survey (USGS) utilized in this study encompasses three months period from 26th January to 26th April 2001. Epicenters of the aftershock are plotted on a map depicting active faults. All the aftershocks of magnitude > 5 and 70% of those ranging between magnitude 3 and 5 are confined to an area resembling a horseshoe pattern with a pointed end towards NE. The other 20% of magnitude 3 to 5 are enclosed within an almost parallel boundary. Only 10% are found to be beyond this limiting boundary. 50% of the recorded aftershocks took place within the first week of the main event and this study reveals that the basic characteristic pattern of aftershock activity can be determined on the basis of the data of only one week. Four major NW-SE trending active faults are mapped in the Kutch region. They define the western limit of Cambay structure and also mark the western limit of Dharangadhra and Wadhwan basins along the SE continuation in Saurashtra. These faults separate the Kutch region into two geologically different blocks. On the SW side the mapped horseshoe pattern gets characteristically truncated along the western most fault, which is characterized by a strike-slip movement in the south and vertical movement in the north. The present study has revealed that the epicenter of the 26th January earthquake is located in the vicinity of the Bhachau township, close to the intersection with the Kutch mainland fault. Furthermore, it has been noticed that most of the epicenters of the aftershock are confined in the intersectional area of the Kutch mainland fault and the NW-SE faults.

Probabilistic Assessment of Earthquake Hazard in Gujarat and Adjoining Region of India

“…The Kachchh basin has the most complete Mesozoic (135-65 Ma) record with a thick accumulation (3000 m) of Late Tertiary to Lower Cretaceous sediments (BISWAS, 1987). Geomorphologically the Kachchh basin can be divided into two main units: The Rann area which becomes inundated by seawater and gradually subsides along major fault zones whereas the other unit comprises high lands which occupy the southern part of Kachchh (MISHRA et al, 2003). (BISWAS, 1987, KARANTH et al, 2001.…”

Geodetic Strain Observations and Return Period of the Strongest Earthquakes of a Given Seismic Source Zone

“…Table 4 shows seismic strain rates of some arbitrary selected significant and medium earthquakes. Data of observed aftershock areas were obtained from MISRA et al (2003), KANAORI AND SHIN-ICHI (1996), HAMDACHE et al (2004) and ZSÍROS (2000. For the earthquake in Komárom (1763) the aftershock area was estimated by use of Eq.…”

Tectonic implications of the earthquakes in the Indian subcontinent

“…Intersection of the two faults (Kutch Mainland Fault and the NW-SE trending marginal faults of the Cambay structure) has been the source area for stress concentration to generate the main shock and the after shocks (Misra et al 2003). But it appears more plausible that the actual displacement has been in NE-SW direction, dextral (more likely) or sinistral.…”