HR: 1340h
AN: T13C-1386    [Abstracts]
TI: Crustal vertical motions from paleogeodetic data of the Sumatran subduction zone, 1950 to 2003: Steady vs. episodic strain accumulation.
AU: * Natawidjaja, D H
EM: danny@geotek.lipi.go.id
AF: California Institute of Technology, Tectonic Observatory 1200 E. California MC 100-23, Pasadena, CA 91125 United States
AU: * Natawidjaja, D H
EM: danny@geotek.lipi.go.id
AF: Pusat Penelitian Geoteknologi - LIPI, GD. 70, Komplek LIPI - Bandung Jalan Sangkuriang no. 21 / 154 D, Bandung 40135, West Java Indonesia
AU: Sieh, K
EM: sieh@gps.caltech.edu
AF: California Institute of Technology, Tectonic Observatory 1200 E. California MC 100-23, Pasadena, CA 91125 United States
AU: Galetzka, J
EM: galetzka@mac.com
AF: California Institute of Technology, Tectonic Observatory 1200 E. California MC 100-23, Pasadena, CA 91125 United States
AU: Suwargadi, B W
EM: bambang.suwargadi@geotek.lipi.go.id
AF: Pusat Penelitian Geoteknologi - LIPI, GD. 70, Komplek LIPI - Bandung Jalan Sangkuriang no. 21 / 154 D, Bandung 40135, West Java Indonesia
AU: Edwards, R
EM: edwar001@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN 55455 United States
AU: Cheng, H
EM: cheng021@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN 55455 United States
AB: We determined submergence/uplift rates from 42 paleogeodetic sites along the 400-km length of the fore-arc islands. Our analysis is based on data of annual lowest low tide levels, which are accurately tracked by the growth patterns of coral microatolls over the past several decades. The annual oceanographic fluctuation is on the order of a few centimeters, and is statistically removed for determinations of average sea-level changes. The average sea-level changes, then, are corrected for the global eustatic sea-level rise to determine the crustal vertical rates. Records from the Batu islands around the Equator show that the sites from 85-km to 115-km northeast from the Sumatran trench are submerging slowly about 1 mm/yr to near zero, where sites closer to the mainland Sumatra are emerging up to 6 mm/yr. The Batu islands are located above the 1935 rupture patch (Mw 7.7). These data constraint an elastic model suggesting that this part of the subduction interface must be predominated by aseismic slips. The paleogeodetic time-series indicate that the subduction in the equatorial region is steady for the past 30 years. Further south from the Equator, the Sipora, North Pagai and South Pagai Islands, where the 1797 and the 1833 historical events (Mw 8.3 and Mw 8.7) had ruptured the interface beneath the islands; the average rates of submergence are generally higher than those of the Batu islands. The rates vary from about more than 10 mm/yr to 2 mm/yr at the sites 90 km to 120 km off the trench. Most of the paleogeodetic time-series of this region indicates that the submergence may be steady, but interrupted by decadal slip events. The Siberut Island, a 110-km length of the fore-arc ridge, located between the 1935 and the 1833 ruptures submerge at a maximum average rate of about 4.5 mm/yr at the middle of the eastern coast, about 110 km from the trench. The rates generally decrease toward the north and the south-end of the island, but are suddenly reverse to very high rates near the strait of the Siberut and Sipora. Numerous fossil microatolls reveal that the Siberut Island raised more than 1 meter during the pre- historical, early 1600s event. Paleogeodetic records of the Siberut sites indicate that the subduction is episodic. That is the long-term fast submergences were interrupted by years of stable periods. The transitions between these fast and near zero submergence are demarcated by (slip) events. One of these events is a major 1962 aseismic slip, which is well documented at numerous sites from the Equator to about 3.5›¦ S. We use these rich data of the upper crustal deformations to investigate the behaviors of the subduction zone in a period after the past major earthquakes and before the next one.
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting