Abstract
The Wharton Basin, off southwest Sumatra, ruptured to a large intraplate left-lateral strike-slip Mw 7.8 earthquake on 2016 March 2. The epicentre was located ∼800 km to the south of another similar-mechanism intraplate Mw 8.6 earthquake in the same basin on 2012 April 11. Small tsunamis from these strike-slip earthquakes were registered with maximum amplitudes of 0.5−1.5 cm on DARTs and 1−19 cm on tide gauges for the 2016 event, and the respective values of 0.5−6 and 6−40 cm for the 2012 event. By using both teleseismic body waves and tsunami observations of the 2016 event, we obtained optimum slip models with rupture velocity (Vr) in the range of 2.8–3.6 km s−1 belonging to both EW and NS faults. While the EW fault plane cannot be fully ruled out, we chose the best model as the NS fault plane with a Vr of 3.6 km s−1, a maximum slip of 7.7 m and source duration of 33 s. The tsunami energy period bands were 4−15 and 7−24 min for the 2016 and 2012 tsunamis, respectively, reflecting the difference in source sizes. Seismicity in the Wharton Basin is dominated by large strike-slip events including the 2012 (Mw 8.6 and 8.2) and 2016 (Mw 7.8) events, indicating that these events are possible tsunami sources in the Wharton Basin. Cumulative number and cumulative seismic-moment curves revealed that most earthquakes are of strike-slip mechanisms and the largest seismic-moment is provided by the strike-slip earthquakes in this basin.
Highlights
A large strike-slip earthquake occurred within the Wharton Basin, offshore southwest of Sumatra, Indonesia on 2016 March 2
The teleseismic waveform-fits between the observed and synthetic waveforms are shown in Supporting Information Figs S1–S3 for three cases of Vr = 2.0, 3.6 and 4.0 km s−1 for the NS fault
Lack of resolution to clearly distinguish between the NS and EW faults can be attributed to the small size of the tsunami and the sparse distribution of the tsunami gauges
Summary
A large strike-slip earthquake occurred within the Wharton Basin, offshore southwest of Sumatra, Indonesia on 2016 March 2. Deep-ocean Assessment and Reporting of Tsunami (DART) gauges recorded amplitudes up to 1.5 cm (Fig. 1d). Lay et al (2016) used seismic records of the 2016 earthquake and reported a bilateral rupture on a NS-striking fault dipping eastward with a velocity of ≤ 2 km s−1 and duration of ∼35 s. Gusman et al (2017) applied a joint teleseismic-tsunami inversion to propose a NS-striking fault dipping westward with a rupture velocity of 2.0 km s−1. The Warton Basin ruptured to other large strike-slip earthquakes in 1928 (Mw 7.7), in 1949 (Mw 6.8), and in 2000 (Mw 7.9) (Fig. 1)
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