A teleseismic finite-fault rupture model for the August 17, 1999, İzmit earthquake (Mw = 7.6): implications for the seismic nucleation phase

Murat Utkucu Murat Utkucu,Hatice Durmuş Hatice Durmuş

doi:10.4401/ag-4954

Abstract

<p>A linear finite-fault inversion procedure is applied to teleseismically recorded broadband P and SH velocity waveforms of the August 17, 1999, İzmit earthquake, to derive spatial and temporal distributions of the co-seismic slip over the representative three-segment model fault. The model fault is longer than the mapped surface rupture, and it extends offshore for 25 km in the west, to define the western end of the earthquake rupture. The teleseismically derived slip model suggests a bilateral rupture with a total seismic moment release of 2.6 ×10<sup>20</sup> Nm, and that the rupture was dominated by failure of two major asperities with peak slip amplitudes reaching 7 m. The hypocentral area was represented by the relatively low displacement that separated the large asperities. In the west, the rupture reached the eastern entrance of the Çınarcık basin beneath the Sea of Marmara, with an average slip of ca. 2 m. This indicates that the rupture propagated offshore for ca. 20 km after crossing Hersek Peninsula. The analysis also reveals that the total rupture process time was 32 s, while the main seismic moment release, which corresponded to the rupture of the two large asperities, occurred between 4 s and 16 s after rupture initiation. The strong wave energy arrivals from the failure of the large asperities were preceded by weak wave arrivals in the initial section of the teleseismic waveforms used in this study. Along with some observations from previous studies, this emergent onset of the wave arrivals prompts us to discuss the possibility of a seismic nucleation process for this earthquake.</p>

Highlights

The North Anatolian Fault Zone (NAFZ) is a 1,500-kmlong dextral transform fault that extends from Karlıova Triple Junction in the east to the northern Aegean Sea in the west [Barka and Kadinsky-Cade 1988, Şengör et al 2005] (Figure 1)
The global positioning system (GPS)-derived crust velocity field has indicated that virtually all of the relative motion of the Eurasian–Anatolian plate was along the NAFZ, with a slip-rate of about 24 mm/yr
By extending the model fault west of the Hersek Peninsula, we explore the location of the western termination of the rupture in the modeling

Summary

Introduction

The North Anatolian Fault Zone (NAFZ) is a 1,500-kmlong dextral transform fault that extends from Karlıova Triple Junction in the east to the northern Aegean Sea in the west [Barka and Kadinsky-Cade 1988, Şengör et al 2005] (Figure 1). It accommodates western extrusion of the Anatolian plate, which is caused by the regional plate kinematics, along with the sinistral East Anatolian Fault Zone [Barka and Kadinsky-Cade 1988, McClusky et al 2000, Reilinger et al 2006]. Both of these strands have resulted in remarkable seismic activity, with tens of large destructive earthquakes through history [Ambraseys and Finkel 1991, Ambraseys 2002], which are exemplified by the destructive August 17, 1999, İzmit (Mw 7.6) and November 12, 1999, Düzce (Mw 7.1) earthquakes (Figure 2)

Objectives

Methods

Discussion

Conclusion