The South Sandwich Islands Earthquake of 27 June 1929: Seismological Study and Inference on Tsunami Risk for the South Atlantic

Research Article| December 01, 2009 THE SOUTH SANDWICH ISLANDS EARTHQUAKE OF 27 JUNE 1929: SEISMOLOGICAL STUDY AND INFERENCE ON TSUNAMI RISK FOR THE SOUTH ATLANTIC E.A. OKAL; E.A. OKAL Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, United States of America, e-mail: emile@earth.northwestern.edu Search for other works by this author on: GSW Google Scholar C.J. HARTNADY C.J. HARTNADY UMVOTO Pty. Limited, Post Office Box 61, Muizenberg, 7950, Cape Provence, South Africa, e-mail: chris@umvoto.com Search for other works by this author on: GSW Google Scholar Author and Article Information E.A. OKAL Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, United States of America, e-mail: emile@earth.northwestern.edu C.J. HARTNADY UMVOTO Pty. Limited, Post Office Box 61, Muizenberg, 7950, Cape Provence, South Africa, e-mail: chris@umvoto.com Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2009 Geological Society of South Africa South African Journal of Geology (2009) 112 (3-4): 359–370. https://doi.org/10.2113/gssajg.112.3-4.359 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation E.A. OKAL, C.J. HARTNADY; THE SOUTH SANDWICH ISLANDS EARTHQUAKE OF 27 JUNE 1929: SEISMOLOGICAL STUDY AND INFERENCE ON TSUNAMI RISK FOR THE SOUTH ATLANTIC. South African Journal of Geology 2009;; 112 (3-4): 359–370. doi: https://doi.org/10.2113/gssajg.112.3-4.359 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract While no large interplate thrust earthquakes are known at the South Sandwich subduction zone, historical catalogues include a number of earthquakes with reported magnitudes of 7 or more. We present a detailed seismological study of the largest one (27 June 1929; MPAS = 8.3). The earthquake relocates 80 km north of the north-western corner of the arc. Its mechanism, inverted through the PDFM method, features normal faulting on a steeply dipping fault plane (φ = 71°, δ = 70°, λ= 272°). The seismic moment, 1.7 x 1028 dyn.cm, supports Gutenberg and Richter's estimate, and is 28 times the largest shallow CMT in the region. The 1929 event is interpreted as representing a lateral tear in the South Atlantic plate, comparable to similar earthquakes in Samoa and Loyalty, deemed "STEP faults" by Govers and Wortel (2005). Hydrodynamic simulations using the MOST method (Titov and Synolakis, 1997) suggest deep-water tsunami amplitudes reaching 30 cm off the coast of Brazil, where run-up should have been observable, and 20 cm along the Gulf of Guinea (Ivory Coast, Ghana). We also simulate a number of potential sources obtained by assigning the 1929 moment to the geometries of other known earthquakes in the region, namely outer-rise normal faulting events at the center of the arc and its southern extremity, and an interplate thrust fault at the southern corner, where the youngest lithosphere is subducted. A common feature of these models is the strong focusing of tsunami waves by the South Atlantic Ridge, the southwest Indian Ocean Ridge, and the Agulhas Rise, resulting in amplitudes always enhanced in Ghana, southern Mozambique and certain parts of the coast of South Africa. This study documents the potential tsunami hazard to South Atlantic shorelines from earthquakes in this region, principally normal faulting events. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.