Global & Disaster Medicine

Archive for the ‘Earthquake’ Category

M 7.2 – 37km NE of Pinotepa de Don Luis, Mexico; Mexico is one of the world’s most seismically active regions.

ShakeMap Intensity image

Estimated Fatalities

Estimated Economic Losses

Seismotectonics of Mexico

Located atop three of the large tectonic plates, Mexico is one of the world’s most seismically active regions. The relative motion of these crustal plates causes frequent earthquakes and occasional volcanic eruptions. Most of the Mexican landmass is on the westward moving North American plate. The Pacific Ocean floor south of Mexico is being carried northeastward by the underlying Cocos plate. Because oceanic crust is relatively dense, when the Pacific Ocean floor encounters the lighter continental crust of the Mexican landmass, the ocean floor is subducted beneath the North American plate creating the deep Middle American trench along Mexico’s southern coast. Also as a result of this convergence, the westward moving Mexico landmass is slowed and crumpled creating the mountain ranges of southern Mexico and earthquakes near Mexico’s southern coast. As the oceanic crust is pulled downward, it melts; the molten material is then forced upward through weaknesses in the overlying continental crust. This process has created a region of volcanoes across south-central Mexico known as the Cordillera Neovolcánica.

The area west of the Gulf of California, including Mexico’s Baja California Peninsula, is moving northwestward with the Pacific plate at about 50 mm per year. Here, the Pacific and North American plates grind past each other creating strike-slip faulting, the southern extension of California’s San Andreas fault. In the past, this relative plate motion pulled Baja California away from the coast forming the Gulf of California and is the cause of earthquakes in the Gulf of California region today.

Mexico has a long history of destructive earthquakes and volcanic eruptions. In September 1985, a magnitude 8.0 earthquake killed more than 9,500 people in Mexico City. In southern Mexico, Volcán de Colima and El Chichón erupted in 2005 and 1982, respectively. Paricutín volcano, west of Mexico City, began venting smoke in a cornfield in 1943; a decade later this new volcano had grown to a height of 424 meters. Popocatépetl and Ixtaccíhuatl volcanos (“smoking mountain” and “white lady”, respectively), southeast of Mexico City, occasionally vent gas that can be clearly seen from the City, a reminder that volcanic activity is ongoing. In 1994 and 2000 Popocatépetl renewed its activity forcing the evacuation of nearby towns, causing seismologists and government officials to be concerned about the effect a large-scale eruption might have on the heavily populated region. Popocatépetl volcano last erupted in 2010.


Taiwan: nine dead and 62 others missing

NY Times

“Many of the missing were believed to be trapped in the 12-story Yun Men Tsui Ti building, which housed a small hotel, apartments and a hot-pot restaurant. About 196 people have been rescued so far from that building and three others.

About 800 people went to bed in shelters on Wednesday….”

 


Taiwan eyewitness: “The Tung-Shuai hotel of Hualian City falls down, very scary!”

Population Exposure Map

PAGER

Estimated Fatalities

Green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

Estimated Economic Losses

Structure Information Summary

Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are unknown/miscellaneous types and adobe block construction.

Secondary Effects

Recent earthquakes in this area have caused secondary hazards such as landslides that might have contributed to losses.


Taiwan: 4 dead, 225 injured, & more than 140 unaccounted for

Chicago Tribune

Magnitude Mw 6.4
Region TAIWAN
Date time 2018-02-06 15:50:43.0 UTC
Location 24.14 N ; 121.72 E
Depth 15 km
Distances 102 km S of Taipei, Taiwan, Province of China / pop: 7,872,000 / local time: 23:50:43.0 2018-02-06
22 km NE of Hualian, Taiwan, Province of China / pop: 351,000 / local time: 23:50:43.0 2018-02-06


2 dead, 173 missing and 219 injured after a magnitude 6.0 earthquake strikes Taiwan

Taiwan News

 


M 6.4 – 22km NNE of Hualian, Taiwan

 

ShakeMap Intensity image

Tectonic Summary

The February 6, 2018, M 6.4 earthquake north-northeast of Hualien, Taiwan, occurred as the result of oblique strike-slip faulting at shallow depth, near the plate boundary between the Philippine Sea and Eurasia plates at the northeast coast of Taiwan. Preliminary focal mechanism solutions for the earthquake indicate rupture occurred on a steep fault striking either east-southeast (right-lateral), or south-southwest (left-lateral). At the location of this earthquake, the Philippine Sea plate converges with the Eurasia plate at a velocity of approximately 75 mm/yr towards the northwest. The location, depth and mechanism of the February 6, 2018 earthquake are consistent with its occurrence on, or along a fault in close proximity and relation to, the complex plate boundary in this region.

Taiwan lies in a region of complex tectonics near the intersection of three major tectonic plates – the Philippine Sea plate to the east and southeast, the Eurasia plate to the north and west, and the Sunda plate to the southwest. The location of the February 6, 2018 earthquake lies near the end of the Ryukyu subduction zone, which marks the plate boundary between the Philippine Sea and Eurasia plates in this region. The plate boundary in Taiwan itself is characterized by a zone of arc-continent collision; whereby the northern end of the Luzon (Philippines) island arc is colliding with the buoyant crust of the Eurasia continental margin offshore China. Along Taiwan’s west coast, and continuing south, this collision zone transitions into the eastward-oriented Manila subduction zone.

The February 6, 2018 earthquake is the largest in a sequence of events in the same region over the past several days. Beginning with a M 4.8 earthquake on February 3, 2018, there have been 19 earthquakes of M 4.5 and larger (as of February 6, 2018, 20:00 UTC). A M 6.1 earthquake occurred as a result of thrust-type faulting on February 4, 2018, just a few kilometers southeast of this M 6.4 earthquake on February 6th.

Because of its plate boundary location, Taiwan commonly experiences moderate-to-large earthquakes. The region within 250 km of today’s earthquake has hosted 184 other M 6+ earthquakes over the preceding century; 25 of these were M 7+. These include a M 7.1 earthquake in September 1922, 25 km to the northeast of the February 6, 2018 earthquake, and a M 7.1 event in March 2002, 55 km to the northeast. The 2002 event resulted in at least 5 fatalities, over 200 injuries, 3 collapsed buildings and the destruction of over 100 houses in the T’ai-pei area. The September 1999, M 7.7 Chi Chi earthquake occurred in central Taiwan, 81 km to the southwest of today’s earthquake. That earthquake resulted in at least 2,297 fatalities, and caused damage estimated at $14 billion.


M 5.8 – 173km W of Ferndale, California

ShakeMap Intensity image

The two morning earthquakes struck two days after a magnitude 7.9 quake in the Gulf of Alaska.


January 24, 1939: An 8.3-magnitude earthquake centered in south central Chile leaves 50,000 people dead and 60,000 injured.

History Channel

 


M 7.9 – 280km SE of Kodiak, Alaska: Tsunami alert

ShakeMap Intensity image

Tectonic Summary

The January 23, 2018 M 7.9 earthquake southeast of Kodiak Island in the Gulf of Alaska occurred as the result of strike slip faulting within the shallow lithosphere of the Pacific plate. Focal mechanism solutions indicate faulting occurred on a steeply dipping fault striking either west-southwest (left lateral) or north-northwest (right lateral). At the location of the earthquake, the Pacific plate is converging with the North America plate at a rate of approximately 59 mm/yr towards the north-northwest. The Pacific plate subducts beneath the North America plate at the Alaska-Aleutians Trench, about 90 km to the northwest of today’s earthquake. The location and mechanism of the January 23rd earthquake are consistent with it occurring on a fault system within the Pacific plate before it subducts, rather than on the plate boundary between the Pacific and North America plates further to the northwest.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Strike-slip-faulting events of the size of the January 23, 2018 earthquake are typically about 230×30 km (length x width).

Large earthquakes are common in the Pacific-North America plate boundary region south of Alaska. Over the preceding century, 11 other M7+ earthquakes have occurred within 600 km of the January 23, 2018 earthquake. Most of these have occurred on the subduction zone interface between the two plates, to the north and northwest of today’s earthquake, including the M 9.2 Great Alaska earthquake of March 1964. The hypocenter of the 1964 event was located about 550 km to the north of the January 23rd earthquake, and the rupture of that event broke much of the shallow subduction zone interface over several hundreds of kilometers. To the southeast of the Alaska Trench, two large (M 7.9 and M 7.8) strike slip earthquakes occurred in November 1987 and March 1988, respectively, several hundreds of kilometers to the east of the January 23, 2018 earthquake. These two earthquakes are not known to have caused any casualties or damage.

 

A tsunami warning is in effect for southeast and south Alaska, including the Alaska Peninsula and Aleutian Islands, as well as British Columbia in Canada. A tsunami watch is in effect for California, Oregon and Washington, according to the Tsunami Warning Center.


M 4.2 – 2km NE of The Geysers, CA

ShakeMap Intensity image

Population Exposure Map

Structure Information Summary

Overall, the population in this region resides in structures that are highly resistant to earthquake shaking, though some vulnerable structures exist. The predominant vulnerable building types are unreinforced brick masonry and reinforced masonry construction.

Secondary Effects

Recent earthquakes in this area have caused secondary hazards such as landslides and liquefaction that might have contributed to losses.


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