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JUAN c U.S. DEPARTMENT OF THE INTERIOR SUMMARY MAP XXX

U.S. GEOLOGICAL SURVEY s Prepared in DE cooperation with the Global a Seismographic FUCA Network

M6.5 Offshore NortheC rn Earthquake of 10 January 2010 PLATE Tectonic Setting 128° 126° 124° 122° 120°

Juan de Fuca Plate Ferndale, California

Oregon 10 January 2010 0:27:38 UTC 9 January 2010 4:27:38 PM Local Time Epicentral Region 124°45' 124°30' 124°15' 40.645° N., 124.763° W. Depth 21.7 km Mw = 6.5 (USGS) Samoa 43 km (E27u rmekilaes) W (280°) from Ferndale, CA 42° 42° 48 km (30 miles) W (259°) from Humboldt Hill, CA 1991 51 km (32 miles) WSW (255°) from Bayview, CA 53 km (33 miles) WSW (252°) from Eureka, CA . 40°45' 40°45'

Fields Landing 2005 NORTH AMERICA PLATE 1980 EXPLANATION

Main Shock Loleta 1922 Douglas M 2.3 - 4.4 Fortuna 1923 City 1994 1992 Earthquake Magnitude Ferndale Rohnerville 5.50 - 5.99 Nevada EPICENTRAL REGION 6.00 - 6.99 1890 40° 40° 7.00 - 7.99 40°30' Rio Dell 40°30' Scotia California 8.00 - 8.99

Reno 9.00 - 9.99 1992 1987

Carson Earthquake Depth 1992 City 1992 0 - 69 70 - 299 S a Citrus n Heights 300 - 700 Petrolia Arden A Town Sacramento n Sacramento US Quaternary Faults d Santa r e Rosa Age of Last Motion RELATIVE PLATE MOTIONS a s 40°15' 40°15' <150 F 124°45' 124°30' 124°15' In the area of this earthquake, the Pacific pate a Vallejo 0 10 20 30 38° moves northward with respect to the North u Richmond 38° <15,000 l Stockton t Concord Km America plate at about 40 mm/yr, and the Oakland Berkeley southern part of the (Gorda <130,000 1906 Oakland Plate) is being subucted beneath the North Daly San Hayward Modesto <750,000 America plate at about 250 mm/yr. Mateo City Fremont Santa <1,600,000 Clara San Jose

128° 126° 124° 122° 120° Significant Mag >= 6.

Scale 1:3,426,777 Year Mon Day Time Lat Long Dep Mag Kilometers 1890 07 26 940 40.5 -124.2 0 6 Seismic Hazard 0 50 100 200 1987 07 31 2356 40.415 -124.407 16 6.0 120° Note on earthquakes: From 1900 - 1963, earthquakes shown are from 1992 04 25 1806 40.368 -124.316 15 7.2 Salem Centennial Catalog, magnitudes greater than 5.5. From 1964 - 2002, 1992 04 26 0741 40.415 -124.603 20 6.6 earthquakes are from HDF catalog, magnitudes greater than 4.5. From 1992 04 26 1118 40.378 -124.575 22 6.7 2003 to present, earthquakes are from NEIC, magnitudes greater than 4.5.

Boise

TECTONIC SUMMARY

This earthquake occurred approximately 35 km WNW of Ferndale, CA in a deformation zone DATA SOURCES Peak Ground of the southernmost Juan de Fuca plate that is commonly referred to as the Gorda plate. The earthquake’s epicenter is northwest of the Mendocino , which is formed by the EARTHQUAKES AND SEISMIC HAZARD Acceleration USGS, National Earthquake Information Center EPICENTRAL REGION intersection of the Mendocino , the and the Cascadia NOAA, National Geophysical Data Center m/sec**2 subduction zone. The Gorda plate is subducting beneath the North America plate at about IASPEI, Centennial Catalog (1900 - 1999) and 2.5-3 cm/year in the direction N50E. The Gorda plate is also subjected to intense extensions (Engdahl and Villaseñor, 2002) compressive stresses by oblique-convergence of the northwestward migrating Pacific Plate as HDF (unpublished earthquake catalog) (Engdahl, 2003) Global Seismic Hazard Assessment Program 40° 40° .2 well as localized eastward spreading at the . The resulting internal deformation .4 of the Gorda plate is manifested primarily by intraplate strike-slip events on vertical NE- Carson PLATE TECTONICS AND FAULT MODEL City .8 oriented faults. PB2002 (Bird, 2003) 1.6 BASE MAP Sacramento Preliminary analysis of the earthquake indicates that it results from slip on a near vertical, NIMA and ESRI, Digital Chart of the World San 2.4 left-lateral fault oriented about N47E. Large strike-slip earthquakes like this one are common USGS, EROS Data Center Francisco 3.2 in the interior of the Gorda plate. There are no reports of this earthquake causing a tsunami. NOAA GEBCO and GLOBE Elevation Models Oakland Strike-slip earthquakes are less likely to produce large tsunamis because they cause relatively San Jose 4.0 little vertical ground displacement. Shaking was strongest near the coast line between REFERENCES 4.8 Petrolia and Eureka, CA, although felt reports for this event extend from as far south and 9.8 north as Capitola, CA and Eugene, OR, respectively, and as far east as Reno, NV. The Bird, P., 2003, An updated digital model of plate boundaries: maximum recorded shaking was observed in Eureka (33%g), which is sufficient to cause Geochem. Geophys. Geosyst., v. 4, no. 3, pp. 1027- 80. moderate damage. Engdahl, E.R. and Villaseñor, A., 2002, Global Seismicity: Seismic hazard is 1900 - 1999, chap. 41 of Lee, W.H.K., and others,eds., expressed as peak This is the largest quake to occur in this region since the April 25, 1992 M7.2 Petrolia and the International Earthquake and Engineering Seismology, ground acceleration June 15, 2005 M7.2 Gorda plate earthquakes. Part A: New York, N.Y., Elsevier Academeic Press, 932 p. (PGA) on firm rock, Los in meters/sec², Engdahl, E.R., Van der Hilst, R.D., and Buland, R.P., 1998, The probability of a strong and possibly damaging aftershock (M>5) in the 7 days following Global teleseismic earthquake relocation with improved trav- Angeles expected to be the earthquake is approximately 78%. Most likely, the mainshock will be the largest in the exceeded in a 50-yr el times and procedures for depth determination: Bull. Seism. Soc. Amer., v. 88, p. 722-743. period with a sequence. However, there is a small chance (~5-10%) of an earthquake equal to or larger than this mainshock in the next 7 days. In addition, numerous M3-5 aftershocks are expected to San probability of 10 occur in the same 7-day period, but most are unlikely to be felt due to the distance from land. DISCLAIMER Diego Mexicali Base map data, such as place names and political 120° boundaries, are the best available but may not be Map prepared by U.S. Geological Survey Scale 1:10,000,000 current or may contain inaccuracies and therefore National Earthquake Information Center should not be regarded as having official significance. 10 January 2010 Kilometers Map not approved for release by Director USGS 0 50 100 200 300