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Published November 26, 2013 | Supplemental Material
Journal Article Open

The February 6, 2013 M_w 8.0 Santa Cruz Islands earthquake and tsunami

Abstract

The Santa Cruz Islands region has high seismicity near a 90° bend in the boundary between the Pacific and Australian plates. Southward, along the Vanuatu island arc, the Australian plate under-thrusts the Pacific plate in a well-defined subduction zone. Westward, a transpressional, predominantly transform boundary extends to the southern Solomon Islands subduction zone. The Santa Cruz Islands region has upper plate strike-slip and normal faulting, plate boundary under-thrusting, outer rise extensional faulting, and intraplate compressional faulting. On February 6, 2013 the largest under-thrusting earthquake (Mw 8.0) that has been instrumentally recorded in the region ruptured the megathrust. The epicenter (10.738°S, 165.138°E) is about 1° north of epicenters of prior large shallow under-thrusting events in Vanuatu in 1934 (M ~ 7.8) and 1966 (MS 7.9), and there is overlap of all three events' aftershock zones, but not their large-slip regions. At least 10 lives were lost, with 6 more missing, due to tsunami ~ 1.5 m high striking the town of Lata and several villages on the main Santa Cruz Island of Nendö (Ndeni) and a nearby small island Nibanga. Inundation of 500 m flooded the Lata airport. The tsunami was well-recorded by DART buoys spanning an unusually wide three-quadrant azimuthal aperture. Iterative modeling of teleseismic broadband P waves and the deep-water tsunami recordings resolves the slip distribution. There are two large-slip patches with a southeastward rupture expansion at about 1.5 km/s, with the second patch appearing to have ruptured with large slip at the trench. The event has relatively low short-period seismic wave energy release, but a typical overall moment-scaled total energy. The shallow rupture depth may be associated with the low level of short-period energy, and a near-total stress drop may account for a lack of underthrusting aftershocks among a highly productive aftershock sequence that included three events with M_w ≥ 7.0.

Additional Information

© 2013 Elsevier B.V. Received 22 March 2013; Received in revised form 29 June 2013; Accepted 2 July 2013; Available online 12 July 2013. This work made use of GMT, SAC and Matlab software. The IRIS DMS data center was used to access the seismic data from Global Seismic Network and Federation of Digital Seismic Network stations. We thank an anonymous reviewer for constructive comments. DART buoy data were obtained from the NOAA National Data Buoy Center. This work was supported by NSF grants EAR-1245717 (T. L.).

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August 22, 2023
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