Global & Disaster Medicine

Archive for the ‘Earthquake’ Category

6.8 earthquake strikes Mindanao island in southern Philippines

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The so-called Loma Prieta earthquake hits the San Francisco Bay Area on October 17, 1989, killing 67 people, injuring 3,757 and causing more than $5 billion in damages.

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M 6.9 – Loma Prieta, California Earthquake

  • 1989-10-18 00:04:15 (UTC)
  • 37.036°N 121.880°W
  • 17.2 km depth
In the Santa Cruz Mountains in the forest of Nisene Marks State Park, about 16 kilometers northeast of Santa Cruz and about 7 kilometers south of Loma Prieta Mountains, California.This major earthquake caused 63 deaths, 3,757 injuries, and an estimated $6 billion in property damage. It was the largest earthquake to occur on the San Andreas fault since the great San Francisco earthquake in April 1906.The most severe property damage occurred in Oakland and San Francisco, about 100 kilometer north of the fault segment that slipped on the San Andreas. MM intensity IX was assigned to San Francisco’s Marina District, where several houses collapsed, and to four areas in Oakland and San Francisco, where reinforced-concrete viaducts collapsed: Nimitz Freeway (Interstate 880) in Oakland, and Embarcadero Freeway, Highway 101, and Interstate 280 in San Francisco. Communities sustaining heavy damage in the epicentral area included Los Gatos, Santa Cruz, and Watsonville.

Liquefaction, as evidenced by sand boils, lateral spreading, settling, and slumping, occurred as far as 110 kilometers from the epicenter. It caused severe damage to buildings in San Francisco’s Marina district as well as along the coastal areas of Oakland and Alameda in the east San Francisco Bay shore area. Liquefaction also contributed significantly to the property damage in the Santa Cruz and Monterey Bay areas, which lie near the epicentral zone. Structures damaged by liquefaction include buildings, bridges, highways, pipelines, port facilities, airport runways, and levees. Subsurface soil conditions, which amplified accelerations in the San Francisco Bay area, strongly influenced structural damage patterns and probably contributed to liquefaction problems in loose, sandy fills underlain by deep, cohesive soil deposits.

Engineered buildings, including those near the epicenter, performed well during the earthquake. Hospital buildings in the region sustained only minor system and cosmetic damage, and operational interruptions did not occur. Only five schools sustained severe damage, estimated at $81 million.

Most of the spectacular damage to buildings was sustained by unreinforced masonry buildings constructed of wood-frame roof and floor systems supported by unreinforced brick walls. These structures failed in areas near the epicenter as well as in areas far from the epicenter, at San Francisco and Monterey. The severe shaking near Santa Cruz caused heavy damage to the unreinforced masonry buildings in that area, particularly in the Santa Cruz Pacific Garden Mall, which consisted of several blocks of unreinforced masonry store buildings.

More than 80 of the 1,500 bridges in the area sustained minor damage, 10 required temporary supports, and 10 were closed owing to major structural damage. One or more spans collapsed on three bridges. The most severe damage occurred to older structures on poor ground, such as the Cypress Street Viaduct (41 deaths) and the San Francisco – Oakland Bay Bridge (one death). Damage to the transportation system was estimated at $1.8 billion.

Most of the more than 1,000 landslides and rockfalls occurred in the epicentral zone in the Santa Cruz Mountains. One slide, on State Highway 17, disrupted traffic for about 1 month.

The earthquake produced a pattern of northwest-trending extensional fractures in the north end of the aftershock zone northwest of the epicenter, but through-going right-lateral surface faulting was not found above the rupture defined by the main shock and its aftershocks. Six feet of right-lateral strike-slip and 4 feet of reverse-slip was inferred from geodetic data. The only surface fracturing that might be attributed to primary tectonic faulting occurred along a trace of the San Andreas near Mount Madonna Road in the Corralitos area, where en echelon cracks showed 2 centimeters of right-lateral displacement.

Extensional fractures (maximum net displacement of 92 centimeters) were observed about 12 kilometers northwest of the epicenter, in the Summit Road-Skyland Ridge area, east of State Highway 17, whereas zones of compressional deformation were found along the northeast foot of the Santa Cruz Mountains between Blossom Hill and Palo Alto. In Los Altos and Los Gatos, ground deformation appeared to be associated closely with zones of heavy structural damage and broken underground utility lines.

Other towns in the area that also experienced severe property damage include Boulder Creek, Corralitos, Hollister, Moss Landing, and several smaller communities in the Santa Cruz Mountains.

This earthquake was felt over most of central California and in part of western Nevada. The rate of aftershock activity decreased rapidly with time, but the total number of aftershocks was less than that expected from a generic California earthquake of similar magnitude. Fifty-one aftershocks of magnitude 3.0 and larger occurred during the first day after the main shock, and 16 occurred during the second day. After 3 weeks, 87 magnitude 3.0 and larger aftershocks had occurred.

Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.

Maximum observed Modified Mercalli Intensity (MMI) IX

M 4.5 Earthquake – 1km SSE of Pleasant Hill, CA

DYFI intensity map

  • 2019-10-15 05:33:42 (UTC)
  • 37.938°N 122.058°W
  • 14.6 km depth


What does a 7.2M earthquake look like in Valparaiso, Chile?

USGS said the quake hit at 10:57 a.m. local time and was centered 40 miles west-southwest of the city of Constitucion and about 225 miles south of Santiago, the capital. The epicenter was 10.3 miles below the surface.

Estimated Fatalities

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

Estimated Economic Losses

Estimated Economic Losses Histogram

Estimated Population Exposure to Earthquake Shaking

Population Exposure Map
Population per ~1 sq. km. from LandScan

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 adobe block and rubble/field stone masonry construction.

Secondary Effects

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

A powerful magnitude 6.8 earthquake shook the coast of Chile on Sunday, swaying buildings in the capital of Santiago. The national emergency agency said there were no reported injuries or damage to basic services.

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At least 37 people were injured on Saturday when a 5.6-magnitude earthquake struck Albania’s central coast near the port city of Durrës

DYFI intensity map

Estimated Fatalities

Estimated Fatalities Histogram
Yellow alert for shaking-related fatalities and economic losses. Some casualties and damage are possible and the impact should be relatively localized. Past yellow alerts have required a local or regional level response.

Estimated Economic Losses

Estimated Economic Losses Histogram
Estimated economic losses are less than 1% of GDP of Albania.

September 21, 1999: An earthquake in Taiwan kills thousands of people, causes billions of dollars in damages and leaves an estimated 100,000 homeless.


The August 29, 2019, M 6.3 earthquake near the coast of Oregon occurred as the result of strike-slip faulting along the Blanco Fracture Zone

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Tectonic Summary

The August 29, 2019, M 6.3 earthquake near the coast of Oregon occurred as the result of strike-slip faulting along the Blanco Fracture Zone, a transform fault marking the boundary between the Pacific Plate to the southwest and the Juan de Fuca Plate to the northeast. Moment tensor solutions show faulting occurred as a result of slip on a steeply dipping fault, either from left-lateral slip on a northeast striking fault or right-lateral slip on a southeast striking fault. Given the moment tensor and orientation of the fracture zone, this event occurred on a steeply dipping, right-lateral, southeast striking fault. At this location, the Juan de Fuca Plate slides past the Pacific Plate at a rate of 49 mm a year along an azimuth of 110 degrees from north. The Juan de Fuca plate ultimately subducts beneath North America along the Cascadia subduction zone about 200 km to the east of today’s event; hence, this earthquake did not occur on the subduction zone, but rather is the result of Pacific:Juan de Fuca plate boundary interactions farther west.

The Pacific-Juan de Fuca Plate boundary offshore of northern California, Oregon, and Washington routinely host moderate size earthquakes. Within 250 km of the August 29th event, there were 21 other earthquakes of magnitude 6 and larger over the preceding 100 years. The largest of these was an M 6.9 earthquake that occurred on July 13th, 1991 that was felt throughout much of western Oregon and northern California. The 1991 event ruptured southeast of the Blanco Fracture Zone, within the Juan de Fuca Plate closer to the coasts of Oregon and northern California. One year prior to this August 29, 2019 earthquake, a similar earthquake in size, location, and mechanism, occurred on August 22, 2019 and was felt along the Oregon coast.

Estimated Fatalities Histogram

Estimated Economic Losses Histogram

7/28/1976: At 3:42 a.m., an earthquake measuring between 7.8 and 8.2 magnitude on the Richter scale flattens Tangshan, China killing an estimated 242,000 people.



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