Natawidjaja, Danny Hilman and Sieh, Kerry and Chlieh, Mohamed and Galetzka, John and Suwargadi, Bambang W. and Cheng, Hai and Edwards, R. Lawrence and Avouac, Jean-Philippe and Ward, Steven N. (2006) Source parameters of the great Sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls. Journal of Geophysical Research B, 111 (B6). Art. No. B06403. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20101117-093202330
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Large uplifts and tilts occurred on the Sumatran outer arc islands between 0.5° and 3.3°S during great historical earthquakes in 1797 and 1833, as judged from relative sea level changes recorded by annually banded coral heads. Coral data for these two earthquakes are most complete along a 160-km length of the Mentawai islands between 3.2° and 2°S. Uplift there was as great as 0.8 m in 1797 and 2.8 m in 1833. Uplift in 1797 extended 370 km, between 3.2° and 0.5°S. The pattern and magnitude of uplift imply megathrust ruptures corresponding to moment magnitudes (M_w) in the range 8.5 to 8.7. The region of uplift in 1833 ranges from 2° to at least 3.2°S and, judging from historical reports of shaking and tsunamis, perhaps as far as 5°S. The patterns and magnitude of uplift and tilt in 1833 are similar to those experienced farther north, between 0.5° and 3°N, during the giant Nias-Simeulue megathrust earthquake of 2005; the outer arc islands rose as much as 3 m and tilted toward the mainland. Elastic dislocation forward modeling of the coral data yields megathrust ruptures with moment magnitudes ranging from 8.6 to 8.9. Sparse accounts at Padang, along the mainland west coast at latitude 1°S, imply tsunami runups of at least 5 m in 1797 and 3–4 m in 1833. Tsunamis simulated from the pattern of coral uplift are roughly consistent with these reports. The tsunami modeling further indicates that the Indian Ocean tsunamis of both 1797 and 1833, unlike that of 2004, were directed mainly south of the Indian subcontinent. Between about 0.7° and 2.1°S, the lack of vintage 1797 and 1833 coral heads in the intertidal zone demonstrates that interseismic submergence has now nearly equals coseismic emergence that accompanied those earthquakes. The interseismic strains accumulated along this reach of the megathrust have thus approached or exceeded the levels relieved in 1797 and 1833.
|Additional Information:||© 2006 American Geophysical Union. Received 3 September 2005; revised 16 January 2006; accepted 17 March 2006; published 16 June 2006. Many friends, colleagues, and family provided critical support of our field efforts in 1999, 2000, 2002, and 2003, particularly Imam Suprihanto, Susi Mardia, and Dudi Prayudi. Maarten Schmidt translated historical Dutch accounts of the earthquakes and tsunamis, and Juniator Tulius found many of them. Jenny Briggs translated the German accounts. Historian Jeffrey Hadler helped us find and interpret historical information. Thorough, thoughtful reviews by Brian Atwater and Harvey Kelsey helped us clarify many points and correct mistakes in the manuscript. Carrie Sieh helped improve the figures. Finally, we are greatly indebted to the many people of mainland West Sumatra and the Mentawai islands for their hospitality and friendship. This research was supported by NSF grants EAR-9628301, EAR-9804732, and EAR-9903301 (to K.S.); EAR-9628716, EAR-9903443, and EAR-0207686 (to R.L.E.); and EAR- 9804970 (to S.N.W.) and by the Indonesian International Joint Research Program (RUTI). This is contribution 15 of the Tectonics Observatory, California Institute of Technology.|
|Group:||Caltech Tectonics Observatory, Caltech Tectonics Observatory. Sumatran Plate Boundary|
|Subject Keywords:||Sumatra; paleoseismology; earthquake|
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|Official Citation:||Natawidjaja, D. H., K. Sieh, M. Chlieh, J. Galetzka, B. W. Suwargadi, H. Cheng, R. L. Edwards, J.-P. Avouac, and S. N. Ward (2006), Source parameters of the great Sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls, J. Geophys. Res., 111, B06403, doi:10.1029/2005JB004025|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||17 Nov 2010 18:28|
|Last Modified:||26 Dec 2012 12:39|
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