Resistivity structure in the western part of the fault rupture zone associated with the 1999 İzmit earthquake and its seismogenic implication

Abstract

Magnetotelluric (MT) surveys were carried out along some profiles crossing the fault rupture zone associated with the Izmit earthquake which took place on 17 August 1999 in the western part of the North Anatolian Fault Zone (NAFZ). In this paper, we focus on the western part of the fault rupture zone where two different groups of seismicity followed the Izmit earthquake. One group was seen along a narrow belt and corresponds to aftershocks occurring along the fault rupture zone. The other was seen in a circular region and represents a swarm activity, presumably triggered by the occurrence of the Izmit earthquake. Two-dimensional inversion was performed for the MT data acquired along two profiles; one crosses the western end of the fault rupture zone and the other is located in the west of the swarm activity area. In the former case, aftershocks tended to occur in a resistive zone underlain by a moderately conductive zone, as was the case for the hypocenter area. In the latter case, the swarm activity tends to be confined in a conductive zone below a highly resistive zone. This activity is likely to be triggered through pore-pressure changes associated with the Izmit earthquake.