1931 Valentine earthquake

Geology

The largest earthquakes in Texas history have occurred in West Texas, which is the state's most seismically active region. Earthquakes have been reported in El Pasonear the state's westernmost extentsince as early as 1887. There are several faults in the region, including the Mayfield Fault, Rim Rock Fault, and Valentine Fault, in addition to other major geologic features such as the Central Basin Platform, the Ouachita Tectonic Front, and the Rio Grande rift. The 1931 Valentine earthquake may have been generated by movement along either the Mayfield or Rim Rock Faults, though no investigation of fault displacement was performed in the area after the earthquake. One 1987 study published in the Bulletin of the Seismological Society of America suggested that the earthquake was caused by either normal or strike-slip faulting at a depth of 6 mi (10 km), with a dip of 54° to the east, a strike of 10–20° and a rake of –150°. The tremor may have resulted in broad subsidence of 4 in (11 mm) over a 10–20 mi (20–30 km) long stretch near Valentine. Though no surface rupture was reported in connection with the earthquake along a fault, cracks in the alluvium within the nearby Quitman Canyon developed during the earthquake, retaining depths of 7 ft and widths as wide as 3 ft at least 17 years after the earthquake.

Earthquake

The main Valentine earthquake occurred at 5:40 a.m. Central Standard Time (11:40 UTC) on August 16, 1931, with an epicenter near , roughly 7 mi (12 km) southwest of Valentine, Texas, and towards the southeastern end of the Rio Grande rift. The earthquake was felt across most of Texas and in portions of Kansas, New Mexico, Oklahoma, and northern Mexico, producing perceptible shaking as far as 400 mi away from the epicenter. Its hypocenter was beneath the Lobo Valley, a northwest-trending alluvial plain. Estimates for its magnitude range between mb 5.6–6.4, making it the strongest earthquake in Texas on record. The United States Geological Survey (USGS) lists the earthquake as having a magnitude of mbLg 5.8 based on the amplitude of short-period surface Lg waves. The ISC–GEM catalogue lists the earthquake as having a magnitude of Mw 6.3. Seismographs as far as St. Louis, Missouri, recorded both foreshocks and aftershocks beginning on August 16 and continuing well after the main earthquake. The foreshocks drove many people to sleep outdoors, possibly mitigating human casualties caused by the main shock. Numerous aftershocks occurred after the main tremor, particularly in the ensuing eight hours. The strongest aftershock occurred at 1:37 p.m. CST (19:37 UTC) on August 18, cracking walls in Valentine and stopping clocks in El Paso. The aftershock had a magnitude of approximately 4.2 and produced a maximum intensity of V (Moderate). A magnitude 3.0 or 3.2 aftershock occurred near Valentine at 9:50 a.m. CST (15:50 UTC) on November 3 and was detected by a seismometer in Tucson, Arizona.

Damage

Shaking from the earthquake was most intense in the Valentine, Texas, area. At Valentine, the shaking intensity reached level VIII (Damaging tremor) on the Rossi–Forel scale and level VIII (Severe) on the Modified Mercalli scale. Every building in the town excluding those made from wood frames sustained damage. Many chimneys toppled or cracked following the quake. The local school facility was damaged beyond repair, and its yard sustained minor cracks. Buildings built with adobe had walls collapse, while wooden structures displayed cracked ceilings. Other walls consisting of concrete, brick, and similar materials had large cracks. Damage also occurred in the counties of Brewster, Culberson, Jeff Davis, and Presidio. While there were no fatalities, some minor injuries resulted from falling adobe. The cost of damage in Valentine amounted to $50,000–$75,000.

Shaking from the earthquake was noticed in the Texas Panhandle, rocking buildings and awakening many people. The Mercalli intensity in Houston was estimated to be as high as III (Weak). The intensity was mild in Ciudad Jiménez, 250 mi (410 km) to the south in Mexico. Although the Houston Post-Dispatch attributed the collapse of homes in Oaxaca City to the Valentine earthquake despite being over 1,080 mi (1,750 km) away from the epicenter, the considerable distance suggested that such effects were caused by a more local earthquake. Several landslides resulted from the tremor. Such incidents took place in the Van Horn Mountains, the Chisos Mountains, southwest of Lobo, near the Big Bend, and to the northwest near Pilares and Porvenir. In New Mexico, the Guadalupe Mountains also hosted landslides; in Picacho, rock- and mudslides were reported. Hydrologic issues occurred in several artificial water bodies, leading to muddied water.

References

References

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