U.S. DEPARTMENT OF THE INTERIOR EARTHQUAKE SUMMARY MAP XXX U.S. GEOLOGICAL SURVEY Prepared in cooperation with the Global Seismographic Network M8.1 Solomon Islands Earthquake of 1 April 2007 Tectonic Setting Epicentral Region 140° 150° 160° 170° 152° 154° 156° 158° 160° 162° Caroline Plate SOLOMON ISLANDS 0° 0° 1 April 2007, 20:39:56 UTC 8.453° S., 156.957° E. North PA C I F I C O C E A N Depth 10 km fixed Bismarck Magnitude = 8.0 (USGS) INDONESIA New Ireland Bougainville South Pacific Plate in Trench An earthquake occurred about 40 km (25 miles) SSE of Gizo, rita P.N.G. Bismarck 6° w B New Georgia Islands, Solomon Islands or about 345 k6m° SOLOMON Ne Kieta (215 miles) WNW of Honiara, Guadalcanal at 2:39 PM MDT, ISLANDS Apr 1, 2007 (Apr 02 at 7:39 AM local time in Solomon Islands). Solomon Sea Plate PAPUA Woodlark Plate 10° NEW GUINEA 10° Choiseul S O L O M O N 95 mm/yr I S L A N D S Balmoral Reef Plate Santa Isabel New 8° 8° VANUATU Hebrides Australia Plate Plate Conway 110 mm/yr Reef Plate 20° 20° EXPLANATION S o l o m o n S e a A U S T R A L I A Mainshock Malaita New Caledonia Mag >= 7.0 Honiara 0 - 65 km Guadalcanal 65 - 300 300 - 600 10° 10° Plate Boundary San Cristobal 140° 150° 160° 170° Subduction RELATIVE PLATE MOTIONS SCALE 1:20,000,000 at the Equator Transform Kilometers The broad red vectors represent the motion 0 200 400 800 1,200 1,600 Divergent of the Australia Plate relative to the other Convergent plates in the region. The motion of the Sa Australia Plate is generally northward with n C respect to the Pacific Plate, and many ris toba micro-plates are caught between them. l Trench EXPLANATION Seismic Hazard 12° 12° 140° 150° 160° 170° Slip (m) Mainshock 0 - 50 152° 154° 156° 158° 160° 162° 50 -100 Aftershocks Scale at the Equator 1:3,500,000 0° 0° Mercator Projection 100 - 150 Earthquake Magnitude Kilometers 150 - 200 0 100 200 400 200 - 250 Jayapura 4.00 - 5.99 250 - 300 New Ireland Finite Fault Model 6.00 - 6.99 Solomon Islands earthquake and 300 - 350 INDONESIA New Britain DISCUSSION tsunami damage photos SOLOMON 7.00 - 7.99 350 - 400 PAPUA Lae Choiseul ISLANDS NEW GUINEA Bougainville 8.00 - 8.99 The Solomon Islands earthquake of April 1, 2007, occurred along the boundary of the Pacific plate with, respectively, the Australia, Woodlark, and Solomon Sea P.N.G. Santa Isabel 3 plates. The latter three plates converge to the east-northeast or northeast against 00 Port 9.00 - 9.99 Moresby Malaita the Pacific plate with velocities of 90-105 mm/y. Along much of the plate 10° 10° boundary between the Pacific plate and the Australia/Woodlark/Solomon Sea Guadalcanal Earthquake Depth plates, relative plate-motion is accomplished principally by subduction of the San Cristobal 0 - 69 Australia/Woodlark/Solomon Sea plates beneath the Pacific plate. The April 1 earthquake’s location and focal mechanism are consistent with the earthquake having occurred as underthrusting of the Australia/Woodlark/Solomon Sea plate D 70 - 299 i CBS online D p beneath the Pacific plate, as part of the broader northeast-directed subduction is 25 CBS online ta ° process. nc N 300 - 700 e or al th on g The Solomon Islands arc as a whole experiences a very high level of earthquake st rik activity, and many shocks of magnitude 7 and larger have been recorded since the e VANUATU 30 early decades of the twentieth century. The April 1 earthquake, however, 5° (N nucleated in a 250-long segment of the arc that had produced no shocks of 5 Townsville 5 magnitude 7 or larger since the early 20th century. W -8 ) ( 0 20° 20° km FINITE FAULT MODEL ) Contributed by A U S T R A L I A Noum'ea Chen Ji, University of California at Santa Barbara ) m EXPLANATION (k New Caledonia Rockhampton DATA SOURCES Distribution of the amplitude and direction of slip for th CBS online p Seismic Hazard subfault elements (small rectangles) of the fault e EARTHQUAKES AND SEISMIC HAZARD D Justin Anderson/Reuters rupture model are determined from the inversion of 0 - 0.2 m/sec**2 USGS, National Earthquake Information Center 0 NOAA, National Geophysical Data Center REFERENCES teleseismic body waveforms. Arrows indicate the 0 .2 - .4 IASPEI, Centennial Catalog (1900 - 1999) and amplitude and direction of slip (of the hanging wall Brisbane extensions (Engdahl and Villaseñor, 2002) Bird, P., 2003, An updated digital model of plate boundaries: with respect to the foot wall); the slip amount is also .4 - .8 HDF (unpublished earthquake catalog) (Engdahl, 2003) Geochem. Geophys. Geosyst., v. 4, no. 3, pp. 1027- 80. color-coded as shown. The view of the rupture plane is Global Seismic Hazard Assessment Program from above. 140° 150° 160° 170° .8 - 1.6 Engdahl, E.R. and Villaseñor, A., 2002, Global Seismicity: PLATE TECTONICS AND FAULT MODEL 1900 - 1999, chap. 41 of Lee, W.H.K., and others,eds., The strike of the fault rupture plane is N55W and the SCALE 1:20,000,000 at the Equator 1.6 - 3.2 Seismic hazard is expressed as peak PB2002 (Bird, 2003) International Earthquake and Engineering Seismology, dip is 25 NE. The dimensions of the subfault elements Kilometers ground acceleration (PGA) on firm Finite Fault Model, Chen Ji, UC Santa Barbara (2007) DISCLAIMER Part A: New York, N.Y., Elsevier Academeic Press, 932 p. are 15 km in the strike direction and 10 km in the dip 0 200 400 800 1,200 1,600 3.2 - 6.4 rock, in meters/sec², expected to be direction. BASE MAP Base map data, such as place names and political Engdahl, E.R., Van der Hilst, R.D., and Buland, R.P., 1998, exceeded in a 50-yr period with a 6.4 - 9.8 probability of 10 percent. NIMA and ESRI, Digital Chart of the World boundaries, are the best available but may not be Global teleseismic earthquake relocation with improved trav- USGS, EROS Data Center current or may contain inaccuracies and therefore el times and procedures for depth determination: Bull. Seism. Map prepared by U.S. Geological Survey NOAA GEBCO and GLOBE Elevation Models should not be regarded as having official significance. Soc. Amer., v. 88, p. 722-743. National Earthquake Information Center 2007 Map not approved for release by Director USGS.