RELOCATION OF LARGE EARTHQUAKES ALONG THE SUMATRAN FAULT AND THEIR FAULT PLANES

In order to identify fault planes of large eartquakes along the Sumatran Fault in Sumatra, western Indonesia, fifteen M ≥ 6.0 earthquakes and their aftershocks, from 1964 to 2011, were relocated using the Modified Joint Hypocenter Determination (MJHD) method. The results of earthquake relocation in northern, central and southern Sumatra for this period, show that the fault planes of M ≥ 6.0 mainshocks, with a few exceptions, were along the Sumatran Fault. We found that in many cases mainshocks originated near the segment boundaries and propagated to the end of the fault segments. The 1967 (M 6.1) and 2003 (M 6.0) earthquakes that occurred in northern Sumatra are off-Sumatran fault earthquakes. We also relocated eleven M ≥ 6.8 earthquakes from 1900 to 1963, and their aftershocks, together with the above-mentioned 15 M ≥ 6.0 earthquakes from 1964 to 2011 in order to obtain precise hypocenter locations of all earthquakes and identify the fault planes of M ≥ 7.0 events. It was possible to relocate hypocenters precisely except for the 1900, 1907 and 1909 events. We found that fault segments related to M ≥ 7.0 events are Kumering for 1933 (M 7.5), Tripa for 1935 (M 7.0) and 1936 (M 7.2), Ketaun for the first event of 1943 (M 7.4), Sumani and Suliti for the second event of 1943 (M 7.6). We considered fault segments related to the 1900 ad 1909 event are Dikit and Siulak, respectively. From the results of earthquake location between 1900 and 2011 and the expected fault lengths of M ≥ 7.0 earthquakes, we obtain earthquake history along the Sumatran fault since the 1892 (M 7.3) event that occurred along the Angkola segment. Possible seismic gaps along the Sumatran Fault are Sunda, Semangko, Manna, Musi, Sianok, Sumpur, Barumun, Toru, Renun, central part of the Tripa, Aceh, and Seulimeum segments.