The 1982 Ometepec earthquake that struck Mexico's southwestern coast near Ometepec (Guerrero) on 7 June was a doublet earthquake that ruptured in two steps. The first happened at 06:52 UTC, the second five hours later at 10:59 UTC. Estimated magnitudes are 6.9 and 7.0 on the Ms scale, and 5.8 and 6.0 on the mb scale.[9] The maximum Mercalli intensities were VII and VIII, respectively.[10]
Mexico's southwestern coast is parallel to the 3,000km (1,900mi) Middle America Trench (MAT), where the oceanic Cocos Plate (a remnant of the ancient Farallon Plate) is being subducted under the North American Plate, resulting in many major earthquakes.[11] Most earthquakes observed in this region are similar to earthquakes seen at other subduction zones, but in the vicinity of Ometepec they tend to occur as doublets.[12] This earthquake is unique in being (circa 2013) the "best documented doublet and for which near and teleseismic data are available", and has been extensively studied.[13]
The interruption of the main rupture that results in a doublet earthquake has been attributed to "asperities", patches in the fault where harder rock resists immediate rupture. However, study of this earthquake's aftershocks shows a discontinuity in their spatial distribution.[14] This has been interpreted as indicating a split in the subducting plate, where the plate is subducting at slightly different down angles on either side of the split.[15]
Yamamoto, Jaime; González-Moran, Tomas; Quintanar, Luis; Zavaleta, Ana B.; Zamora, Araceli; Espindola, Victor H. (January 2013), "Seismic patterns of the Guerrero–Oaxaca, Mexico region, and its relationship to the continental margin structure", Geophysical Journal International, 192 (1): 375–389, Bibcode:2013GeoJI.192..375Y, doi:10.1093/gji/ggs025.
The 1976 Songpan–Pingwu earthquake that struck Songpan and Pingwu counties in Sichuan, China consisted of three mainshocks on the 16th, 21st, and 23rd (UTC) of August. A 1984 report gave the magnitudes as 7.2, 6.7, and 7.2, respectively. The magnitudes were subsequently recalculated as 6.7, 6.3, and 6.4 on the Mw scale, and 7.0, 6.6, and 6.7 on the Ms scale. These were preceded by an earthquake swarm lasting three years. During the period from August 16 to August 31 there were over 400 aftershocks of magnitude 3.0 or greater.
The 2008 Iceland earthquake was a doublet earthquake that struck on 29 May at 15:46 UTC in southwestern Iceland. The recorded magnitudes of the two main quakes were 5.9 Mw and 5.8 Mw , respectively, giving a composite magnitude of 6.1 Mw . There were no human fatalities, but injuries were reported and a number of sheep were killed. The epicenter of the earthquake was between the towns of Hveragerði and Selfoss, about 45 kilometers (28 mi) east-southeast of the capital, Reykjavík. It was the strongest earthquake to hit Iceland since the summer of 2000.
The 2009 West Papua earthquakes occurred on January 4 local time in Indonesia's Tambrauw Regency in Southwest Papua. The very large earthquake doublet comprised a Mw 7.6 initial shock that had a maximum Mercalli intensity of VI (Strong) and a second event measuring Mw 7.4 and a maximum Mercalli intensity of VII. The events took place less than three hours apart to the east-northeast of Sorong on the Bird's Head Peninsula and left at least four people dead and dozens injured.
The 1995 Neftegorsk earthquake occurred on 28 May at 1:04 local time on northern Sakhalin Island in the Russian Far East. It was the most destructive earthquake known within the current territory of Russia, with a magnitude of Ms7.1 and maximum Mercalli intensity of IX (Violent) that devastated the oil town of Neftegorsk, where 1,989 of its 3,977 citizens were killed, and another 750 injured.
The 1995 Colima–Jalisco earthquake occurred on October 9 at 15:35 UTC with a moment magnitude of 8.0 and a maximum Mercalli intensity of VIII (Severe). The shock occurred off the coast of Jalisco, Mexico, where a tsunami was triggered that affected a 200 km (120 mi) stretch of the coast. The earthquake could be felt in Mexico City and in high-rise buildings in Dallas and Houston. In Mexico, the Cihuatlan-Manzanillo was the most severely affected area. At least 49 people died and 100 were injured.
The 2010 Oaxaca earthquake struck Oaxaca, Mexico on June 30, 2010, with an Mw magnitude of 6.3. Many people in different cities left their beds and ran into the street, as the quake struck at 2:22 am. Helicopters and police vehicles were sent to inspect possible damage in Mexico City, primarily in downtown and central areas, where some buildings were evacuated. In Mexico City, some cases of power outage in Azcapotzalco, Iztapalapa, and Benito Juárez and cracks in buildings were reported. 1 person died in San Andrés Huaxpaltepec, Oaxaca.
The 2010 Mindanao earthquakes occurred in the southern Philippines in the Moro Gulf. This was a complex sequence of events including three main events of Mw magnitude 7.3 or greater on the 23rd of July, and two significant aftershocks of magnitude 6.6 on the 24th and 29th. All of these were deep focus earthquakes, at depths from 565 km (351 mi) to 634 km (394 mi). This resulted in minimal, but very widespread shaking at the surface, with a maximum intensity of IV on the PEIS scale; consequently there were no reports of casualties or damage.
The 1997 Harnai earthquake occurred on February 27 at 21:08 UTC near Harnai, Pakistan, and felt throughout much of central Balochistan, with a magnitude estimated at 7.0 on the Mw scale. A 2016 study determined that this was a doublet earthquake, the Mw 6.8 shock that hit 19 seconds later being a continuation of the initial main shock. The largest aftershock was an Ms 6.4 shock that hit 22 minutes after the main shock. The earthquake was caused by the collision between the Indian Plate and the Eurasian Plate.
The 1937 Orizaba earthquake occurred on July 26 at 03:47 UTC, near Orizaba, Veracruz, Mexico. It had a magnitude of 7.3 on the surface wave magnitude scale. Thirty four people were reported dead. Damage was reported in Esperanza, Puebla. This was an intraplate earthquake within the subducting Cocos Plate.
The 1971 Solomon Islands earthquakes occurred in the northern part of the Solomon Islands, within Papua New Guinea as a doublet earthquake. The first large shock occurred on July 14 at 06:11 UTC with a magnitude of Mw 8.0. The second large event occurred on July 26 at 01:23 UTC with a magnitude of Mw 8.1. The initial event on July 14 caused a tsunami, which was observed in Rabaul. The earthquake of July 26 triggered a tsunami with a 3.4 m (11 ft) runup in New Britain.
The 1932 Jalisco earthquakes began on June 3 at 10:36 UTC with a megathrust event that registered 8.1 on the moment magnitude scale. With a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale, at least 400 deaths were caused in Mexico and neighboring Guatemala. It was the first of a series of seismic events that affected parts of western Mexico during the month of June 1932, all reaching magnitude 7 or greater.
The 2012 Guerrero–Oaxaca earthquake struck southern Mexico with a moment magnitude of 7.4 at 12:02 local time on Tuesday, 20 March. Its epicenter was near Ometepec, in the border between the states of Guerrero and Oaxaca. With a shallow focus of 20 km, the earthquake caused strong shaking over a large area along the Oaxaca–Guerrero border and the adjacent Pacific coastline. Significant tremors were felt in areas up to several hundred kilometers away, including Mexico City and also in Guatemala. Two people were killed and over 30,000 houses were damaged or destroyed.
The 1942 Guatemala earthquake occurred at 17:37 local time on August 6 and had ratings of 7.7 on the moment magnitude scale and 7.9 on the surface wave magnitude scale. The epicenter was located off the southern coast of Guatemala, and it was one of the strongest earthquakes ever recorded there.
The 1981 Playa Azul earthquake occurred on October 24, 1981, at 21:22 local time. It was located near Playa Azul, Michoacán, Mexico. The magnitude of the earthquake was Mw 7.2, or Ms 7.3. Three deaths were reported, two from Michoacán and one from Mexico City. Some buildings were damaged in both Michoacán and Mexico City. A small tsunami was registered in Acapulco with a maximum height of 9 cm.
The 1990 Vrancea earthquakes were three earthquakes on 30 and 31 May 1990 with magnitudes of 7.0 Mw and 6.2 Mw that struck the Romanian county of Vrancea, on two consecutive days. Severe damage in the Bucharest-Brăila-Brașov area was reported and dozens of casualties in Romania and neighbouring Moldova, Ukraine and Bulgaria.
The 1976 Longling earthquake in Yunnan Province, People's Republic of China, was a doublet earthquake, with two main shocks striking just east of Longling at 12:23:20 and 14:00:22 UTC. The magnitudes were estimated at 6.7 and 6.6, respectively, on the Mw(GCMT) scale, and 6.9 and 7.0 on the Ms scale; Chinese sources put these at 7.4 and 7.3 on the Ms7 scale. The region is noted for the quantity and intensity of its earthquakes, and the complexity of its tectonics, which are closely related to the collision between the Indian and Eurasian tectonic plates.
The 1957 Guerrero earthquake occurred on 28 July at 08:40 UTC. It had a magnitude of 7.6 Mw and a maximum perceived intensity of VII on the Modified Mercalli intensity scale. Mexico City and Chilpancingo were particularly badly affected. It caused the deaths of between 54 and 160 people. A small tsunami was triggered but caused little damage.
On January 30, 1973, at 15:01 (UTC–6), a magnitude 7.6 earthquake struck 35.3 km (21.9 mi) beneath the Sierra Madre del Sur range in the Mexican states of Colima, Jalisco and Michoacán. On the Mercalli intensity scale, the earthquake reached a maximum intensity of X (Extreme), causing serious damage in the region. At least 56 people were killed and about 390 were injured. The event is commonly referred to as the Colima earthquake.
The 1920 Xalapa earthquake was the deadliest in Mexico's history prior to 1985—killing at least 648 people. It occurred on January 3 at 22:25 local time, during a period of political unrest in the country. Mudflows and landslides triggered by the shock destroyed buildings in rural towns across the states of Veracruz and Puebla, causing most of the deaths. The earthquake was attributed to a shallow fault in the Trans-Mexican Volcanic Belt. It measured moment magnitude 6.3–6.4 and had a hypocenter depth of <15 km (9.3 mi). The Mexican government took immediate action in the aftermath—providing assistance and establishing communication services. Severely damaged towns including Xalapa were rebuilt, while others had to be abandoned. Help to survivors also came from civil society groups, civilians, and the Catholic Church. The earthquake's aftershocks were studied by scientists to determine its seismological characteristics.
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