U.S. DEPARTMENT OF THE INTERIOR EARTHQUAKE …...Jansen Koehler Segundo Cokedale Trinidad Boncarbo...

Map prepared by U.S. Geological Survey National Earthquake Information Center 2005 Map not approved for release by Director USGS DATA SOURCES EARTHQUAKES AND SEISMIC HAZARD USGS, National Earthquake Information Center NOAA, National Geophysical Data Center IASPEI, Centennial Catalog (1900 - 1999) Handbook of Seismology and Earthquake Engineering Global Seismic Hazard Assessment Program PLATE TECTONICS Smithsonian Institution, Global Volcano Program BASE MAP NIMA and ESRI, Digital Chart of the World USGS, EROS Data Center EARTHQUAKE SUMMARY MAP XXX U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY DISCLAIMER Base map data, such as place names and political boundaries, are the best available but may not be current or may contain inaccuracies and therefore should not be regarded as having official significance. Seismic hazard is expressed as peak ground acceleration (PGA) on firm rock, in meters/sec², expected to be exceeded in a 50-yr period with a probability of 10 percent. M5.0 New Mexico Earthquake of 10 August 2005 Sangre de Christo Range Sangre de Christo Range San Juan Mountains San Louis Valley Rio Grande Rift COLORADO NEW MEXICO TEXAS OKLAHOMA 2004 2004 2001 2001 1971 1970 1970 1966 1966 1960 1955 1948 1947 1944 1935 1918 1893 1878 Portales Clovis Hereford Las Vegas Santa Fe Trinidad Pueblo Canon City Fountain Colorado Springs Castle Rock Parker 107° 107° 106° 106° 105° 105° 104° 104° 103° 103° 102° 35° 35° 36° 36° 37° 37° 38° 38° 39° 39° Seismotectonic Setting COLORADO NEW MEXICO TEXAS OKLAHOMA Portales Clovis Hereford Albuquerque Rio Rancho Las Vegas Santa Fe Trinidad Pueblo Canon City Fountain Colorado Springs Castle Rock Parker 2004 2004 2001 2001 1971 1970 1970 1966 1966 1962 1961 1960 1960 1955 1948 1947 1944 1935 1935 1931 1918 1893 1878 107° 107° 106° 106° 105° 105° 104° 104° 103° 103° 102° 35° 35° 36° 36° 37° 37° 38° 38° 39° 39° Seismic Hazard Map EXPLANATION M5.0 Earthquakes M3 - 3.9 M4 - 5.7 Historical Earthquakes Intensity > = 5 Age of Faults <10,000 yr <130,000 <750,000 Quaternary Seismic Hazard 10-15 9-10 8-9 7-8 6-7 5-6 4-5 3-4 2-3 1-2 0-1 0 100 200 300 50 Kilometers 0 100 200 300 50 Kilometers Sangre de Christo Mountains COLORADO NEW MEXICO Raton Vigil Hebron Valdez Sopris Weston Jansen Koehler Segundo Cokedale Trinidad Boncarbo Stonewall Starkville 105°10'0" 105°10'0" 105° 105° 104°50'0" 104°50'0" 104°40'0" 104°40'0" 104°30'0" 104°30'0" 36°40'0" 36°40'0" 36°50'0" 36°50'0" 37°0'0" 37°0'0" 37°10'0" 37°10'0" NEW MEXICO 2005 August 10 22:08:17 UTC 36.960°N, 104.855°W, Depth 5.0 Km Mw=5.0 A moderate earthquake occurred at 22:08:17 (UTC) on Wednesday, August 10, 2005. The magnitude 5.0 event has been located in NEW MEXICO. Felt (III) at Cimarron, Questa and Raton. Felt (IV) at Aguilar, Trinidad and Weston, Colorado. Also felt at Colorado Springs, Fort Garland, La Junta, Lamar, La Veta, Olney Springs and Pueblo, Colorado. 0 10 20 30 40 5 Kilometers Projection UTM Zone 13 Scale 1: 250,000 DISCUSSION The August 10, 2005, earthquake occurred in the southern Rocky Mountains near the Colorado-New Mexico border, about 40 km (20-30 mi) southwest of Trinidad. The earthquake occurred within a broad region of extensional tectonic stress that is associated with the highlands of the intermountain states and that extends west from westernmost Great Plains to the Pacific coastal states. Earthquakes within the broad zone typically occur as the result of normal faulting or strike-slip faulting. The August 10, 2005, earthquake occurred as the result of slip on a north-striking normal fault. The August 10 mainshock was preceded by approximately 20 small, instrumentally recorded, earthquakes that occurred beginning in 2001, and whose calculated locations are close enough to the August 10 epicenter that they may have been on the same fault. Few of the earlier shocks were reported felt, and none are known to have caused damage. In addition to previous earthquakes that may have occurred on the same fault, a swarm of small earthquakes occurred in September 2001 several tens of kilometers northeast of the August 10, 2005, shock. The locations and focal mechanism of the September 2001 earthquake swarm imply that those shocks also occurred on a normal fault, but the fault that produced the September 2001 earthquake swarm had a northeasterly rather than northerly strike. The largest earthquake in the 2001 swarm had M 4.6 and produced minor damage. The southern Rocky Mountains and adjacent Great Plains in general have been characterized by a moderately low level of earthquake activity, substantially lower than in some parts of the intermountain states to the west, but higher than in many sections of the Great Plains farther to the east. Throughout the highlands of the western United States, the largest earthquakes have tended to occur on major faults that outcrop on the earth’s surface, but small and moderate shocks commonly occur on faults that are too small or situated too deep in the earth’s crust to be mapped even retrospectively, after the earthquakes have occurred. A major, active, geologic fault has not been mapped in the immediate vicinity of the epicenter of the August 10 shock. The shock was situated 50 km east of the Rio Grande rift, a 1000 km long north- south zone of major normal faults where east- west tectonic extension has been concentrated within the past few millions of years. Geologic evidence indicates that large prehistoric earthquakes have produced surface ruptures on many of the Rio Grande rift faults in the late Pleistocene (10,000 to 130,000 years ago) or Holocene (within the last 10,000 years). The August 2005 shock likely reflects the same regional extensional stress field that has produced, and will continue to produce, occasional larger shocks on faults of the Rio Grande rift. EXPLANATION Epicenter M5.0 Earthquakes M3 - 4 M4 - 5.7 Significant Earthquakes Intensity > = 5 or Mag >= 4 Age of Faults <15,000 <130,000 <750,000 Quaternary Historical and Significant Earthquakes Intensity >= 5 or Mag >= 4.0 Year Mn Dy Lat Long Mag 1878 06 14 36.50 -104.90 1893 04 08 34.50 -106.80 1893 09 07 34.50 -106.80 1918 05 28 35.50 -106.00 1931 02 05 35.10 -106.60 1935 02 21 34.50 -106.80 1935 12 16 34.70 -106.80 1935 12 18 34.70 -106.80 1935 12 20 34.70 -106.80 1944 09 09 39.00 -107.50 1947 11 06 35.20 -106.30 1948 03 12 36.22 -102.48 4.5 1955 08 03 38.00 -107.30 1960 07 23 34.35 -106.85 1966 01 23 36.98 -107.02 5.1 1966 10 03 37.40 -104.10 4.6 1970 11 02 35.89 -103.40 3.5 1970 11 28 35.10 -106.61 4.5 1971 01 04 35.10 -106.60 4.7 2001 08 09 39.66 -107.38 4.0 2001 09 04 37.14 -104.65 4.0 2001 09 05 37.14 -104.62 4.5 2002 01 31 40.29 -107.69 4.3 2004 03 22 36.85 -104.85 4.4 2004 05 23 32.53 -104.57 4.0 2004 08 01 36.87 -105.10 4.4 2005 08 10 36.96 -104.86 5.0

U.S. DEPARTMENT OF THE INTERIOR EARTHQUAKE …...Jansen Koehler Segundo Cokedale Trinidad Boncarbo...

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