Coupling Between the 1999 M7+ Ruptures in Turkey as Illuminated by Small Earthquakes

Abstract for proposal EAR-0087798 (PH #48x)

Title: Coupling Between the 1999 M7+ Ruptures in Turkey as Illuminated by Small Earthquakes

PI's: L. Seeber and J. G. Armbruster, Lamont-Doherty Earth Observatory

The Mw 7.4 Kocaeli (Izmit) earthquake on 17 August 1999 was followed on 12 November 1999 by the Mw 7.2 Duzce earthquake, which extended the rupture extent of the first earthquake eastward. We deployed a 10 station network covering the junction between these two ruptures from 1 week after the first earthquake to 3 months after the second, and recorded ~30,000 events. We are leading an effort to form a single phase-data set from all of the stations that were deployed in this study area. This catalog will then be used to map seismogenic faults, monitor regional elastic and poroelastic effects and observe S-wave splitting in space and time.

Research objectives include:

1) understanding the role of secondary faults and of strain partitioning in the complex transtensional tectonic regime of the western North Anatolian transform and in the triggering of successive mainshocks in the sequence;

2) testing whether the second mainshock was triggered directly by the first mainshock or whether it was triggered by a strain event closer in space and time to the site of rupture nucleation; and

3) investigating whether S-wave splitting can be used to monitor mechanical changes associated with both rupture and healing of the fault zone and stress changes in the surrounding medium. This study is a collaboration with Kandilli Observatory of Bogazici University and Istanbul University.