Rupture Kinematics of the 2005Mw 8.6 Nias–Simeulue Earthquake from the Joint Inversion of Seismic and Geodetic Data

Abstract

The 2005 M w 8.6 Nias-Simeulue earthquake was caused by rupture of a portion of the Sunda megathrust offshore northern Sumatra. This event occurred within an array of continuous Global Positioning System (GPS) stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture. Thus, this earthquake provides a unique opportunity to assess the source characteristics of a megathrust event from the joint analysis of seismic data and near-field static co-seismic displacements. Based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip, where the dip is determined to be 8Њ to 10Њ with corresponding moments of 1.24 ‫ן‬ 10 22 to 1.00 ‫ן‬ 10 22 N m, respectively. The geodetic constraints on slip distribution help to eliminate the trade-off between rupture velocity and slip kinematics. Source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long-period seismic waveforms (100-500 sec). Our results indicate a relatively slow average rupture velocity of 1.5 to 2.5 km/sec and long average rise time of up to 20 sec. The earthquake nucleated between two separate slip patches, one beneath Nias and the other beneath Simeulue Island. The gap between the two patches and the hypocentral location appears to be coincident with a local geological disruption of the forearc. Coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accretionary prism. Using the models from joint inversions, we estimate the peak ground velocity on Nias Island to be about 30 cm/sec, an order of magnitude slower than for thrust events in continental areas. This study emphasizes the importance of utilizing multiple datasets in imaging seismic ruptures.

Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011

“…velocity model), the method assumes implicitly that the major part of afterslip and the seismicity occurs on or close to (Hsu et al 2006) and aftershocks shown for the same 11 months period after the mainshock. Grey lines indicate co-seismic slip distribution (2.5-m slip contours, Konca et al 2007). the subduction interface.…”

A 15 year slow‐slip event on the Sunda megathrust offshore Sumatra

“…These added observations allow us to model the possible locations and sizes of this SSE, both with improved constraints. [Konca et al, 2007]. Part of this section ruptured during the 2010 M w 7.8 Banyak Islands earthquake (source model from the U.S. Geological Survey: http://earthquake.usgs.gov/earthquakes/ eventpage/usp000hat0#scientific_finitefault).…”

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake

“…One fundamental question which this paper seeks to answer is: Can seismic data provide sufficiently accurate models of the slip distributions of large tsunamigenic earthquakes to be reliably used in teletsunami modelling? While both seismic (KIKUCHI and KANAMORI, 1991) and tsunami (SATAKE, 1987) data are routinely used separately to estimate slip distributions for large earthquakes, they are rarely used together (see, however, SATAKE, 1993;TANIOKA et al, 1995;JOHNSON et al, 1996;KONCA et al, 2007;SATAKE and TANIOKA, 1995;DELOUIS et al, 2002;KOKETSU et al, 2004;ICHINOSE et al, 2005 andCHLIEH et al, 2007, for examples of joint inversion using various combinations of seismic, tsunami and geodetic data). One reason for this is that tsunami data have hitherto been taken from coastal tide gauges, which can be very sensitive to the shallow bathymetry in their immediate vicinity.…”