U.S. DEPARTMENT OF THE INTERIOR EARTHQUAKE SUMMARY MAP U.S. GEOLOGICAL SURVEY Middle Andaman Prepared in cooperation with the Global Seismographic M8.6 Northern , Earthquake oSouth fAnda man11 April 2012 Network A n d a m a n B a s i n Tectonic Setting Little Andaman Epicentral Region 90° 100° EURASIA PLATE 110° 92° 94° 96° 98° 100° PAGER Ranong 10° 10° INDIA ANDAMAN SEA Car Nicobar Surat T H A I L A N D Thani

V I E T N A M Nakhon Si B A Y O F C A M B O D I A Phangnga Thammarat

B E N G A L 1941 Krabi 2010 A N D A M A N 8° Phuket 8° Gulf Phatthalung 10° S E A of S O10U° T H Trang Thailand BURMA 1881 C H I N A Songkhla PLATE S E A Pattani S R I L A N K A Satun Yala Kangar Alor Setar 6° 6° M A' A Banda L A Aceh 2004 Y S u m a t r a F a u l t Pinang 2004 S I A 2005 M i d - I n d i a n B a s i n S I N G A P O R E S Ipoh 1861 u 0° EPICENTRAL m 0° a REGION 2005 tr a 4° 4° I N D O N E S I A Medan 1833 EXPLANATION 2004 Great Rupture AUSTRALIA 2007 PLATE J AVYAea rS E A

GreateRru pStuuren Zdoane Islands 2010

I 2005 n 1907

AUSTRALIA PLATE v Mag ≥ 7.0 1969

e e 2° Depth Profile Area 2°

J0a - v6a9 km s g

t

d 70 - 299

i

g i S a U 300 - 600 R

t N

10° RELATIVE PLATE MOTIONS o D A1c0t°ive Volcanoes

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r A In the region of this earthquake, ( s J A earthquakes define the boundary R AVA a ) T between the Sunda Plate and the i RENC Northern Sumatra Earthquake d H

E Burma and Australia plates, which g 11 April 2012 8:38:37 UTC are converging at about 52 mm/yr. e Pini y t 0° 2.348° N., 93.072° E. 0°

e 1935 90° 100° 110° EXPLANATION Depth 25 km n Mw = 8.6 (USGS) i Scale 1:15,000,000 Tanahbala O s b o r n Earthquakes 1900 - 2012 2009

P l a t e a u N Km M 5.50 - 5.99 Northern Sumatra Earthquake 1943 0 500 1,000 Padang M 6.00 - 6.99 S u m a t r a DATA SOURCES Seismic Hazard 11 April 2012 10:43:09 UTC Siberut 90° 100° M 7.00 - 7.99 Significant Earthquakes Mag >= 7.5 0.773° N., 92.4522° E. EARTHQUAKES AND SEISMIC HAZARD Bassein Moulmein Phitsanulok Khon Savannakhet Hue Rangoon Nakhon Depth 16 km Year Mon Day Time Lat Long Dep Mag USGS, National Earthquake Information Center Kaen Da Nang M >= 8.00 Sawan Ubon Quang Mw = 8.2 (USGS) 1907 01 04 0519 2.000 94.500 50 7.5 NOAA, National Geophysical Data Center Nakhon Ratchathani Ngai 2° 2° IASPEI, Centennial Catalog (1900 - 1999) and Ratchasima Aftershocks 1935 12 28 0235 -0.345 98.147 35 7.8 LAOS 1943 06 09 0306 -1.000 101.000 50 7.5 extensions (Engdahl and Villaseñor, 2002) THAILAND Sipora HDF (unpublished earthquake catalog) (Engdahl, 2003) Tavoy Play Cu Earthquake Depth 2007 1969 11 21 0205 1.973 94.574 11 7.6 Samut Prakan Global Seismic Hazard Assessment Program Bangkok Siemreab Qui Nhon 0 - 69 2004 12 26 0058 3.295 95.982 30 9.0 Samut Buon Me Batdambang 2005 03 28 1609 2.085 97.108 30 8.6 Sakhon Thuot VIETNAM N Pagai PLATE TECTONICS AND MODEL 70 - 299 2007 09 12 1110 -4.438 101.367 34 8.5 Port Phnom Da Lat PB2002 (Bird, 2003) Nha 300 - 700 (event not on Epicentral Map) Blair CAMBODIA Penh Ho Chi Finite Fault Model, Chen Ji, UC Santa Barbara (2007) Trang S Pagai 2007 09 12 2349 -2.625 100.841 35 7.9 Rupture Zone World Slap (Hayes and Wald, 2010) Bien HoaMinh City 2010 2009 09 30 1016 -0.720 99.867 81 7.5 Tan An Phan Vinh Long Active Volcanoes 2010 04 06 2215 2.383 97.048 31 7.8 10° Rach Gia My Tho Thiet 10° BASE MAP Can Tho 2010 06 12 1926 7.881 91.936 35 7.5 NIMA and ESRI, Digital Chart of the World Bac Lieu Soc 4° 4° Nakhon Si Trang 2010 10 25 1442 -3.487 100.082 20 7.8 USGS, EROS Data Center Thammarat 92° 94° 96° 98° 100° 2012 04 11 1043 0.773 92.452 16 8.2 NOAA GEBCO and GLOBE Elevation Models

MALAYSIA Earthquakes locations are from the Centennial Scale 1:4,840,000 Songkhla Catalog (1900-2003) and from NEIC (2003-present) Km Kota EPICENTRAL Alor Yala REFERENCES Banda Setar Baharu 0 100 200 400 REGION Kuala Aceh Pinang Terengganu Bird, P., 2003, An updated digital model of plate boundaries: Ipoh Geochem. Geophys. Geosyst., v. 4, no. 3, pp. 1027- 80. Kuantan Enggano New Port Medan Kuala Engdahl, E.R. and Villaseñor, A., 2002, Global Seismicity: Lumpur Depth Profile 1900 - 1999, chap. 41 of Lee, W.H.K., and others,eds., Seremban International Earthquake and Engineering Seismology, Melaka A Distance (km) A' TECTONIC SUMMARY Part A: New York, N.Y., Elsevier Academeic Press, 932 p. Johor -300 -200 -100 0 100 200 300 400 500 600 Baharu Singapore Engdahl, E.R., Van der Hilst, R.D., and Buland, R.P., 1998, Pekanbaru The April 11, 2012, M8.6 and M8.2 earthquakes off the west coast of northern Sumatra, Indonesia, occurred as a Global teleseismic earthquake relocation with improved trav- Pontianak result of strike-slip faulting within the oceanic lithosphere of the Indo-Australia plate. The quakes were located 0° 0° 0 0 el times and procedures for depth determination: Bull. Seism. respectively 100 km and 200 km to the southwest of the major zone that defines the plate boundary Padang Soc. Amer., v. 88, p. 722-743. between the India/Australia and Sunda plates offshore Sumatra. At this location, the India/Australia plates move Jambi Peak Ground north-northeast with respect to the Sunda plate at a velocity of approximately 52 mm/yr. The GEBCO_08 Grid, version 20090202, http://www.gebco.net ) m

Acceleration k -100 -100 Palembang ( Hayes, Gavin, and Wald, David, 2010, Slab models for Large strike-slip earthquakes are not unprecedented in the diffuse boundary region separating the India and h m/sec**2 Bengkulu t subduction zones: USGS, Australia plates, southwest of the Sumatra subduction zone. Since the massive M 9.1 earthquake that ruptured a p http://earthquakes.usgs.gov/research/data/slab 1300 km long segment of the Sumatran megathrust plate boundary in December of 2004, three earlier large strike- e .2 Tanjungkarang- D Telukbetung slip events had occurred within 50 km of the first large April 11, 2012 event. These earthquakes occurred on April -200 -200 DISCLAIMER .4 Jakarta 19 2006 (Mw6.2), October 4 2007 (Mw6.2) and January 10, 2012 (Mw7.2). The focal-mechanisms of the three Scale 1:15,000,000 earlier earthquakes and the two great earthquakes of April 11, 2012, are consistent in implying that each .8 Bandung Base map data, such as place names and political earthquake could have occurred as the result of left-lateral slip on a north-northeast striking fault or right-lateral 1.6 Km boundaries, are the best available but may not be slip on a west-northwest striking fault. The two different orientations of strike-slip faulting are both possible under -300 -200 -100 0 100 200 300 400 500 600 current or may contain inaccuracies and therefore 2.4 0 200 400 600 the same tectonic stress field; perpendicular strike-slip faults that are both compatible with the same stress field are should not be regarded as having official significance. 3.2 Earthquakes within the Depth Profile are those whose epicenters that lie within the rectangle centered on line A-A' in the called “conjugate faults.” Possibly faults of both orientation have been involved in the recent earthquake activity. "Epicentral Region" map. 4.0 Map prepared by U.S. Geological Survey National Earthquake Information Center 10° 10° 4.8 11 April 2012 Map not approved for release by Director USGS 9.8

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