2010 Baja California earthquake

Geology

The quake originally was believed to have occurred on the Laguna Salada Fault, which is about 60–80 km long and straddles the California–Baja California border.

By the distribution of aftershocks and using radar interferometry, the main shock rupture was found to have occurred on a previously unmapped fault in the Cucapah Mountains and beneath the Colorado River Delta. This fault line was named the Indiviso Fault, after the nearby town of El Indiviso. A liquefaction zone bounded by the Cerro Prieto Fault and the Laguna Salada Fault was observed.

Timeline

Foreshocks

Mexicali, El Centro, San Diego, Ensenada, and Tijuana are situated in a very active seismic zone and surrounded by important faults. An earthquake of such magnitude had been expected around the fault situated in the southeast of Mexicali. Before the 7.2 earthquake occurred, the surrounding area had been seismically active in 2009. Several foreshocks began from April 1, 2010, with magnitudes of 3 and 4.

Mainshock

The earthquake measured 7.2 on the moment magnitude scale that started 25 km south of Guadalupe Victoria, Baja California, at a depth of 10 km. It occurred at 22:40 UTC (15:40 local time) on Easter Sunday, April 4, 2010, and it is said to have lasted about a minute and 29 seconds. Since the earthquake occurred on this day, it has been also called the Easter Sunday earthquake. Intensity VII (Very strong) shaking was felt in Calexico, Imperial, El Centro, and Heber. Intensity VI (Strong) shaking was felt in the Imperial Valley towns of Ocotillo, Calipatria, Brawley, and Holtville.

The April 4 quake was the second largest earthquake in Baja California history after the 1892 Laguna Salada earthquake at a magnitude of 7.2–7.8 on the Richter magnitude scale, and was well recorded in Southern California, especially in the Imperial valley.

Aftershocks

Four aftershocks with a magnitude of at least 5 have been reported; one at a magnitude of 5.2, one at 5.4, one at 5.1, and one at a magnitude of 5.7, all four within one hour. Additionally, a 5.3 aftershock hit the region very close to the mainshock epicenter on April 8, at approximately 9:44 AM local time. There have been at least nine large aftershocks in total.

By six hours after the earthquake, more than 90 aftershocks or triggered earthquakes between magnitude 3.0 and 5.1 were recorded in northern Baja California and Southern California. This included a magnitude 3 event 5 km off the coast of Malibu, California. By the early hours of the following morning, scientists had measured 100 aftershocks.

Pat Abbott, a professor emeritus of geology at San Diego State University, said, "Any quake of this size seems to pass some kind of threshold where it's large enough to disturb or trigger other faults. In cases like this, that often means increasing stress on other faults, which makes them more prone to movement. The energy seems to be moving northward toward the San Andreas Fault. I don't want to anthropomorphize, but it's like this quake was goading the San Andreas." It remains to be seen how the 1300 km San Andreas Fault was affected by these temblors. The southern section of the San Andreas Fault worries scientists, because it has not ruptured in more than 300 years. The region also includes other faults, including the Imperial Fault Zone.

In the early morning hours of April 10, 2010, an aftershock measuring magnitude 4.4 was felt throughout most of Southern California and Baja California. It was said to have lasted about ten seconds. No injuries or damage were reported. Another aftershock measuring a similar magnitude struck Southern California on the morning of April 11.

Seismologists in the California Institute of Technology of Pasadena announced a 10 percent chance of another earthquake on the same magnitude (7.3) or greater to strike within the first week, and 5 percent in the rest of the month of April 2010. It also falls on the state of California's Earthquake Preparedness month, as state and FEMA officials urge the state citizens to take preparations, and schools and businesses conduct earthquake drills across the state. The California Geological survey added 50 new faults to its map of faults several weeks after the earthquake.

Geological field work as of April 5, 2010, by Dr. Thomas Rockwell, professor of geology at San Diego State University, indicates about one meter of right-lateral surface faulting and 0.3 to 0.5 meters of vertical road offset on a fault that is located east of Laguna Salada Fault. Whether or not this is the Cerro Prieto Fault is unclear as of April 5. This is a developing field situation, as geologists are working to locate and measure the lateral extent of the surface faulting.

A strong aftershock with a magnitude of 5.7 occurred on June 14, 2010, at 9:26:58 PM PDT, with an epicenter near Ocotillo in southwestern Imperial County and a focal depth of 5.0 km.

On July 7, 2010, a 5.4-magnitude earthquake, triggered by the April 10, 2010, quake, occurred on the San Jacinto Fault, the most seismically active fault in California, and one of two that exhibited signs of increased pressure following the Mexico quake. It was centered 15 miles (20 kilometers) northwest of the town of Borrego Springs. The main quake in April had transferred stress to fault zones farther north, triggering the aftershock. The quake rattled buildings in downtown Los Angeles, toppled bottles off shelves, and briefly halted rides at Disneyland.

Impact

Mexico

Baja California state capital Mexicali was reported by Comisión Federal de Electricidad (CFE) Director General Alfredo Elías Ayub as being without electricity. There were at least two fatalities in Mexicali, At least 100 people were injured in Mexicali and its suburbs. Multiple fires were caused by ruptured natural gas lines and damaged propane tanks, and people were stuck in collapsed buildings as of the day after the quake. Major damage to irrigation systems occurred, severely impacting over 80,000 acres of agriculture in the Mexicali Valley. Groundwater flowed to the surface, flooding fields and damaging hundreds of miles of irrigation canals. 25,000 people overall were impacted by the earthquake.

CNN reported that, "Pictures from Mexicali showed the sides ripped off buildings, toppled telephone poles, cracked roads, and supermarket aisles strewn with food that had fallen off shelves." and windows were broken at the Chamber of Commerce in the city. According to the San Diego Union Tribune, the largest hospital in Mexicali sustained damage and was moving patients to other facilities.

The quake was felt for about 40 seconds in Tijuana, Baja California, located 174 km to the west-southwest, where it caused buildings to sway and knocked out power in parts of the city. Families celebrating Easter ran out of the homes. A falling tree damaged a city water tank. The earthquake cracked the main aqueduct that carries Colorado River water from Mexicali to Tijuana, causing limitations on the water supply in Tijuana.

The day after the quake, Baja California Governor José Guadalupe Osuna asked the federal government for a state of emergency to be declared. President Felipe Calderón visited the Mexicali area on Monday, April 5, to inspect the damage first-hand.

United States

United States Geological Survey seismologist Dr. Lucy Jones said at least 20 million people in the United States and Mexico, including most of Southern California, felt the quake. Skyscrapers shook in San Diego, California, 180 km northwest of the epicenter. The earthquake broke at least two water mains, one at a Nordstrom department store in Fashion Valley Mall and another at Mission Bay High School. The Coronado Bridge over San Diego Bay was briefly closed by the California Highway Patrol as a precautionary measure. The Sheraton Hotel and Marina was evacuated when cracks were discovered in the floors and reoccupied once deemed to be safe.

Electric service was disrupted across most of the Imperial Valley.

In El Centro, California, gas leaks, water main breaks, and collapsed chimneys and balconies were reported. A man was injured when he fell during the quake, and another man was injured when a sign fell on him. One city hospital had so many people, that The Salvation Army sent a truck with water canteens and sandwiches.

It was felt in downtown Los Angeles, and in a Century City high-rise in Los Angeles. The rides in Disneyland were temporarily closed for inspection. In the Yuma, Arizona area, 3,369 residents experienced a "relatively momentary [power] outage" from the quake, "but most were back in service shortly afterward".

References

References

1. The active Laguna Salada Fault ruptured in February 1892 with an estimated {{M. w
2. Naranjo, Laura. (November 20, 2011). "Baja's Fault". NASA EOSDIS.
3. "M72-el-major-cucapa-quake | Alaska Satellite Facility".
4. (April 4, 2010). "El sismo se esperaba hace tiempo: experto". Diario Rotativo.
5. Chang, Alicia. (April 4, 2010). "Big Baja quake came from 'chaotic' fault system". The Mercury News.
6. (April 4, 2010). "Strong 6.9 quake jolts Baja California, Mexico". Yahoo.
7. Denny, Barbara. (April 4, 2010). "Easter Sunday Earthquake in Baja California Felt Strongly in Coronado". eCoronado.com.
8. "M7.2 – Baja California, Mexico". United States Geological Survey.
9. (April 5, 2010). "Resumen Tectónico". United States Geological Survey.
10. "Magnitude 5.2 – Baja California, Mexico". United States Geological Survey.
11. "Magnitude 5.4 – BAJA CALIFORNIA, MEXICO". United States Geological Survey.
12. "Magnitude 5.1 – SONORA, MEXICO". United States Geological Survey.
13. Kleske, Andrew. (April 8, 2010). "More Mexican earthquakes shake San Diego region".
14. (April 4, 2010). "90+ aftershocks in Mexico-California region after strong quake". Digital Journal.
15. (April 4, 2010). "One death reported in Baja quake". Los Angeles Times.
16. (April 5, 2010). "Police patrol quake-damaged Calif. border town". Fox News.
17. Lafee, Scott. (April 5, 2010). "Temblor could disturb faults, scientists say". The San Diego Union-Tribune.
18. Wayland, Michelle. (April 11, 2010). "Weekend Aftershocks Rattle San Diego". NBC San Diego.
19. (April 28, 2010). "Map shows 50 new California faults". Los Angeles Times.
20. Robbins, Gary. (June 14, 2010). "Late night quake jolts San Diego". The San Diego Union-Tribune.
21. (June 14, 2010). "Preliminary Earthquake Report Magnitude 5.8 SOUTHERN CALIFORNIA". United States Geological Survey.
22. (April 4, 2010). "Elevan a 7.2 grados Richter temblor en BC". [[El Universal (Mexico City).
23. (April 4, 2010). "Magnitude 7.2 Quake Hits Baja, Mexico, Shakes L.A. (Update3)". [[Bloomberg Businessweek]].
24. (April 5, 2010). "Two killed, 100 injured in Mexican earthquake". CNN.
25. Orr, Katie. (April 5, 2010). "7.2 Earthquake Rocks Mexicali, San Diego Region". KPBS.
26. Gracia, Alan Dennis. (Nov 14–17, 2011}}{{dead link). "Irrigation Engineering in Seismic Zones – Mexicali Valley, Mexico".
27. Isackson, Amy. (April 25, 2010). "Mexicali Earthquake Reshapes Lives And Landscape". KPBS.
28. (April 4, 2010). "Reportan un muerto por sismo de 7.2 en BC". [[El Universal (Mexico City).
29. (April 4, 2010). "Earthquake shakes Pacific coast". CNN.
30. (April 4, 2010). "Mexico Earthquake 2010: 7.2 Quake Hits Baja California, Shakes Los Angeles". HuffPost.
31. (April 5, 2010). "Magnitude 7.2 quake blamed in Baja deaths". The San Diego Union-Tribune.
32. (April 5, 2010). "Gobernador pide declarar desastre en BC". [[El Universal (Mexico City).
33. Tony Perry, Tracy Wilkinson and Ching-Ching Ni. (April 5, 2010). "After quake, life calms down on both sides of U.S.-Mexico border".
34. (April 4, 2010). "7.2 Earthquake Shakes San Diego Region".
35. Vives, Ruben, Shelby Grad. (April 4, 2010). "6.9 earthquake strikes Baja California; Los Angeles rattled". Los Angeles Times.
36. (April 4, 2010). "Magnitude 7.2 Earthquake Reported in Baja California". Fox News.
37. (April 4, 2010). "ImperialValleyPressOnline". Imperial Valley Press.
38. Perry, Toni, Tracy Wilkinson. (May 4, 2010). "Quake rolls across Baja".
39. Steinhauer, Jennifer. (April 4, 2010). "Strong Mexico Quake Shakes Buildings and Nerves in California". The New York Times.
40. Wood, Daniel. (April 4, 2010). "Mexicali earthquake: What are the damage reports in LA?". [[The Christian Science Monitor]].
41. (April 4, 2010). "Baja California Earthquake Felt in Arizona". [[KSAZ-TV.
42. (April 6, 2010). "Cuatro muertos y cien heridos por sismo en Baja California". CNN.
43. Gonzalez-Ortega, Alejandro. (2014). "El Mayor-Cucapah (Mw 7.2) earthquake: early near-field postseismic deformation from InSAR and GPS observations". Journal of Geophysical Research.
44. National Geophysical Data Center / World Data Service (NGDC/WDS). (1972). "Significant Earthquake Database". [[National Geophysical Data Center]], [[National Oceanic and Atmospheric Administration.
45. "The Mw 7.2 El Mayor Cucapah (Baja California) Earthquake of April 4, 2010". EERI Special Earthquake Report.