Seismic history and seismotectonics of the Sunda Arc

Abstract

Historic records of the last 300 years reveal two great interplate earthquakes (1833, MW = 8¾ 1861, MW = 8¼–8½), which ruptured major segments of the Sumatra fore arc in western Indonesia; a significant percentage of interplate slip along this portion of the plate boundary appears to occur seismically. The ends of these rupture zones are coincident with clusters of large (Ms ≥ 7) and moderate (6 ≤ Ms ≤ 7) shocks and with heterogeneities in the plate interface as inferred from geologic and geophysical data. The northern extent of the 1833 rupture zone is coincident with a group of moderate and large earthquakes, a structural arch in the fore arc, and a fracture zone on the subducted plate. The southern portion is coincident with a very prominent cluster and the along‐strike extension of a sediment‐filled trough on the subducted plate. Prior to this study, Sumatra was characterized as relatively aseismic as inferred from the lack of great earthquakes in the instrumental record of this century. Java and the Lesser Sunda Islands had major (Ms ≥ 6) earthquakes in the historic record, but none are of the same magnitude as the great events near Sumatra. There is no clear evidence that shocks in the Java fore arc were interplate events, yet geophysical data indicate recent uplift of the trench slope break and a change in strike of the trench axis where the northernmost flank of the Roo Rise, a prominent bathymetrie high, appears to be interacting with the fore arc. This feature was formed at a ridge crest and is more buoyant, and thus more difficult to subduct, than the surrounding seafloor. There is no increase in seismicity associated with this tectonism, however, that may indicate a lack of contact between the crystalline portions of the plates at this time. We infer that a majority of slip on the plate interface near Java occurs aseismically. The variation in occurrence of great interplate earthquakes along the Sunda Arc may be interpreted in terms of a model that attributes variation in interplate coupling to the age of the subducted lithosphere. Great interplate earthquakes occur near Sumatra, where the age of the youngest crust is 46 Ma. The characteristics of the Sunda Arc, and analogies with Pacific arcs, imply that the entire length of Sumatra has the potential to produce great thrust earthquakes; its seismic potential should be considered high (as there has been no recurrence of the great events of 1833 and 1861). In contrast, no such events have been reported off Java and the Lesser Sunda Islands, where the oldest crust is 152 Ma. The plate interface near Java and the Lesser Sunda Islands should be considered to have low seismic potential.

Discovery of possible mega-thrust earthquake along the Seram Trough from records of 1629 tsunami in eastern Indonesian region

“…The Pacific Plate moves WNW and sideswipes the northern part of the Banda Arc at a rate of 110 mm/year. Blue stars-epicentral locations and magnitudes of earthquakes mentioned in the paper nearly the same area estimated by Newcomb and McCann (1987) from accounts in the Wichmann catalog of an earthquake and tsunami in 1861.…”

What happened and what's next?

“…It will be necessary to learn how the Sumatran parts of the megathrust are segmented structurally, and how they have behaved in the past. Immediately south of the 2004 rupture, for example, it appears from the historical record that there were very large earthquakes in 1861 and 1907 10 .Where on the megathrust were these ruptures, and how often and how regularly do they recur? Palaeoseismic data are available only for a 700-km-long section farther away, from about 1ᑻ to 5ᑻ south of the Equator.…”

Planktic Foram Dates from the Indonesian Arc: Marine 14C Reservoir Ages and a Mythical AD 535 Volcanic Eruption

“…No major historical Indonesian earthquakes recorded before 1883 were centered near Sunda Strait, and severe shaking from the 1875 Central Java event probably did not extend as far west as the core site (Newcomb and McGann 1987). Seismicity associated with the 1883 eruption was only moderate, but the slump may be attributable to a local earthquake in 1880, which was strong enough to cause severe damage to the lighthouse on Java's First Point at the southern end of the strait (Verbeek 1885).…”

“…The resulting violent tectonic activity has included numerous large volcanic and seismic events (Newcomb and McGann 1987;Simkin and Siebert 1994), some involving tens to hundreds of thousands of fatalities and catastrophic damage to infrastructure. These disasters include the 1815 VEI (Volcanic Explosivity Index) 7 eruption of Mount Tambora in the Lesser Sunda Islands east of Java (Self et al 1984), the 1883 VEI 6 eruption of Krakatau in Sunda Strait between Java and Sumatra (Verbeek 1885), and the 26 December 2004 M=9.1 Aceh earthquake off northern Sumatra and the resulting Indian Ocean tsunami (Lay et al 2005).…”