Source complexity of the 1988 Armenian Earthquake: Evidence for a slow after‐slip event

Abstract

We analyzed teleseismic P and S waves using a multiple‐event deconvolution method to investigate the source process of the Spitak, Armenia, earthquake of December 7, 1988. Teleseismic long‐period body waves exhibit complex waveforms, significantly more complex than those normally seen for an event of this size. We identified two groups of subevents. One is a group of strike‐slip events during the first 20 s. The other is a dip‐slip event initiating at about 30 s after the initial rupture. The tensor sum of all the subevents is essentially strike‐slip (strike=302°, dip=59°, rake=143°) with a scalar moment of 1.47×1019 N m. The seismic moment of the dip‐slip event (strike=89°, dip=60°, rake=88°) is 5.6 ×1018 N m, nearly 40% of the total, and the moment release rate is slower than the other subevents with a strike‐slip mechanism. We call this event a slow after‐slip event. The mechanism of the after‐sup event is consistent with the present‐day deformation pattern in the Caucasus where north‐south compression is predominant due to the continental collision between the Arabian plate and the Russian Platform. This result suggests that in a region where both strike slip motion and crustal shortening are taking place, like southern California, a large strike‐slip event may accompany large thrust events and vice versa. In order to determine the total coseismic deformation pattern, it is essential to resolve these multiple events in time, space, and mechanism.

Fault source model for the 2016 Kumamoto earthquake sequence based on ALOS-2/PALSAR-2 pixel-offset data: evidence for dynamic slip partitioning

“…8). Therefore, independently from the JMA's moment tensor, the slip distributions at distinct segments in our fault model suggest that both normal faulting and strike-slip earthquakes have simultaneously occurred in a single event (Kawakatsu 1991;Kikuchi et al 1993) and that no source volume changes occurred; we may call it dynamic slip partitioning. While Kawakatsu (1991) interpreted the non-double couple components in earthquakes at ridge-transform faults as simultaneous occurrence of both normal and strike-slip at transform faults, our fault model would be the first geodetic evidence for the simultaneous rupture hypothesis of non-double couple component with no volume changes.…”

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

“…M is the solution vector composed of the N sub-faults. The Kikuchi and Kanamori method, which is based on a finite fault and the non-negative least square method, was used to restore the rupture scenario by fitting the observed waveform to the synthetic one in a time domain [10][11][12][13]. In order to obtain a stable solution, a smooth constraint was added alongside the non-negative prerequisite to keep the slip ratio of the neighbored sub-fault below a preset constant.…”

Reawakening of large earthquakes in south central Chile: The 2016 Mw 7.6 Chiloé event

“…The backprojection method shows a unilateral emission of radiated energy bursts extending towards the north of the epicenter for almost 30 km ( Figure S2). The slip inversion using teleseismic data [Kikuchi et al, 1993] shows a simple rupture patch of 20 km radius and short rupture duration and a seismic moment equivalent to M w 7.5 ( Figures S5 and S6). We inverted the static displacements obtained from GPS receivers in GUAG, MELK, QLLN, and RMBA, using a uniform isotropic medium with rigidity 45 GPa and Poisson's ratio 0.25 and the slab model proposed by Tassara and Echaurren [2012].…”