A Comparative Study of the Sumatran Subduction-Zone Earthquakes of 1935 and 1984

Abstract

A M s 7.7 earthquake struck the western, equatorial coast of Sumatra in December 1935. It was the largest event in the region since the two devastating giant earthquakes of 1833 and 1861. Historical seismograms of this event from several observatories around the world provide precious information that constrains the source parameters of the earthquake. To more precisely quantify the location, geometry, and mechanism of the 1935 event and to estimate the coseismic deformation, we analyze the best of the available teleseismic historical seismograms by comparing systematically the records of the 1935 earthquake with those of a smaller event that occurred in the same region in 1984. First we constrain the source parameters of the 1984 event using teleseismic records. Then, we compare the records of the 1935 event with those of 1984 from the same sites and instruments. To do this, we choose several time windows in the corresponding seismograms that contain clearly identifiable phases and deconvolve the modern event from the older one. The deconvolutions result in very narrow pulses with similar sizes, thus confirming similar locations and mechanisms for the events. The initiation of the 1984 event was on the subduction interface at a depth of 27 ‫ע‬ 2 km; its M 0 is 6.5 ‫ן‬ 10 19 N m (M w is 7.2). The sense of slip was nearly pure thrust, on a plane dipping 12Њ. The 1935 event also involved rupture of the shallow subduction interface, but was about five times larger (M 0 3.3 ‫ן‬ 10; 20 N m, M w 7.7) and initiated a few kilometers to the southeast, along strike. The 1935 rupture propagated unilaterally toward the southeast. The along-strike rupture length was about 65 km. From these source parameters, we calculate the surface deformations, assuming an elastic multilayered medium. These deformations compare favorably with those actually recovered from paleoseismic data in the form of coral microatolls.

Coseismic Slip and Afterslip of the GreatMw 9.15 Sumatra–Andaman Earthquake of 2004

“…The Nias segment, located between Simeulue Island and the Batu Islands, broke in 1861 (M w ϳ8.5) (Newcomb and McCann, 1987) and again during the M w 8.6 28 March 2005 event (Briggs et al, 2006;Hsu et al, 2006;Kreemer et al, 2006b;Konca et al, 2007). The Batu Islands segment near the Equator, where the Investigator Fracture Ridge enters the subduction zone, has produced only moderate interplate events with magnitude less than 7.7 (Rivera et al, 2002;Natawidjaja et al, 2004). South of the equator, beneath the Mentawai Islands, a couplet with magnitudes estimated at M w ϳ8.5-9.0 occurred in 1797 and 1833 (Zachariasen et al, 1999;Sieh et al, 2004;Natawidjaja et al, 2006).…”

The Sumatra subduction zone: A case for a locked fault zone extending into the mantle

“…In central Sumatra, two major thrust events occurred in 1833 (M $ 9) and 1861 (M $ 8.5), which may have ruptured the subduction interface to depths of the order of 40-50 km [Newcomb and McCann, 1987] (Figure 2). More recently, the 1935 (M w 7.7) and 1984 (M w 7.2) thrust events ruptured smaller patches of the subduction interface at the boundary between the 1833 and 1861 earthquakes [Rivera et al, 2002] ( Figure 2); the ruptured surface involved in both recent events extended to depths greater than the 27 km deep Figure 2. Location of study area.…”

Seismic parameters re-determined from historical seismograms of 1935-Erdek–Marmara Island and 1963-Çınarcık Earthquakes

“…Usually the information necessary for all the process of the analyzing of these records, such as instrument constants and time accuracy, is missing or doubtful (Batlló et al 2008;Kanamori 1988;Abe 1994). The importance of studying historical earthquakes by analyzing original records through the modern techniques has been realized by many researchers over the world (e.g., Baskoutas et al 2000;Dineva et al 2002;Kanamori et al 2010;Lee et al 1988;Pino et al 2000Pino et al , 2008Schlupp 1996;Schlupp and Cisternas 2007;Stich et al 2003Stich et al , 2005Teves-Costa et al 1999;Cadek 1987;Abe 1994;Rivera et al 2002;Kikuchi et al 2003), which presented different methods and stimulated to carry out more comprehensive investigations about historical earthquakes over the world.…”