Abstract
In the subduction zone off the west coast of central Sumatra, two great earthquakes, the 2007 great Bengkulu earthquake (Mw 8.4) and the 2010 Mentawai tsunami earthquake (Mw 7.8), occurred along the plate interface. Although the moment magnitude of the 2010 earthquake was much smaller than that of the 2007 earthquake, the tsunami heights resulting from the former 2010 earthquake were higher than those resulting from the latter 2007 earthquake, indicating that tsunami heights are difficult to forecast. An advanced method for determining appropriate source models that can explain the tsunami heights along coastal areas is needed for tsunami warning purposes. In this study, fault parameters were estimated from the W-phase inversion, and fault length and width were calculated from suitable scaling relations between those and the magnitude for the 2007 and 2010 earthquakes. Tsunami numerical simulations were conducted using various slip amounts or corresponding rigidities. The best slip amount or corresponding rigidity was selected by comparing the measured and computed tsunami heights. For the 2007 Bengkulu earthquake, the measured tsunami heights are well explained using a rigidity of 3.0 × 1010 Nm−2 (7.59-m slip amount). For the 2010 Mentawai tsunami earthquake, the measured tsunami heights are well explained using a rigidity of 1.5 × 1010 Nm−2 (8.17-m slip amount). From those results, we determined the depth-dependent rigidity relation for Central Sumatra to estimate appropriate source models in our tsunami height forecasting method.
Highlights
The subduction of the Indo-Australian plate beneath the Eurasian plate off the west coast of Sumatra has often resulted in large tsunamigenic earthquakes
We knew that the earthquake occurred along the subducted plate interface, the centroid location of the W-phase inversion off the trench was used to estimate the best fault model for the tsunami forecast to test how well the measured tsunami heights along the coast were explained
Our result shows that the tsunami computed from the best fault model, even though it is incorrectly located off the trench, agrees well with the measured tsunami heights along Mentawai Islands
Summary
The subduction of the Indo-Australian plate beneath the Eurasian plate off the west coast of Sumatra has often resulted in large tsunamigenic earthquakes. On September 12, 2007, a great earthquake (Mw 8.4) occurred offshore the Bengkulu province of Sumatra. The mainshock generated a large tsunami along the Bengkulu coastline and caused damage at several locations in the Bengkulu coastal area (Borrero et al 2009). A few years later, another large earthquake (Mw 7.8) occurred on October 25, 2010, off the west coast of Mentawai Islands at 21:42 local time (14:42 UTC). This earthquake generated a large tsunami and caused more than 400 casualties around the Mentawai Islands.
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