Loma Prieta USA 1989 (SPA)

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Event ID
198910180004
Event name
Loma Prieta
Country
USA
Epicentral coordinates (long/lat)
POINT(-121.88 37.04)
WKT GIS format
GEMECD contributing partner
SPA
Event narrative

The magnitude 6.0, October 17, 1989 (California time) Loma Prieta earthquake occurred 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.

It was the largest earthquake to occur on the San Andreas fault since the great San Francisco earthquake in April 1906.

The earthquake produced a pattern of northwest-trending extensional fractures in the north end of the aftershock zone northwest of the epicenter, but throughgoing 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.

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.

Date of occurrence (UTC)
1989-10-18
date
Time of occurrence (UTC)
00:04:15
time
Date of occurrence (local)
1989-10-17
date
Time of occurrence (local)
17:04:15
time
Day of the week (local)
Tuesday
Magnitude
6.9
Magnitude units
Moment (Mw)
Focal depth
18
km
Seismological data: source
USGS
Overall impact

This major earthquake caused 63 deaths, 3,757 injuries, and an estimated $6 billion in property damage. The most severe property damage occurred in Oakland and San Francisco, about 100 kilometers north of the fault segment that slipped on the San Andreas.

Modified Mercalli intensity IX was assigned to San Francisco's Marina District, where several houses collapsed and fires ensued, 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 transpotation 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.

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.

(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)

Overview data
Loss: Human Casualty
show
hide
People injured
3757
number
People injured: source
EERI
People injured: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.


People seriously injured
521
number
People seriously injured: source
USGS
People seriously injured: comment

Durkin, M. E., Thiel, C.C. and Schneider, J.E. (1994) "Casualties and Emergency Medical Response", in Loss Estimation and Procedures, The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response, Prof. Paper 1553-A, U.S. Geological Survey, Washington


People missing
3
number
People missing: source
EERI
People missing: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.


People killed
65
number
People killed: source
USGS
People killed: comment

Durkin, M. E., Thiel, C.C. and Schneider, J.E., "Casualties and Emergency Medical Response", in Loss Estimation and Procedures, The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response, Prof. Paper 1553-A, U.S. Geological Survey, Washington; note that EERI Spectra Ch. 11 notes that this was later revised to 62, but no other information.


People killed due to ground shaking
57
number
People killed due to ground shaking: source
USGS
People killed due to ground shaking: comment

Durkin, M. E., Thiel, C.C. and Schneider, J.E. (1994) "Casualties and Emergency Medical Response", in Loss Estimation and Procedures, The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response, Prof. Paper 1553-A, U.S. Geological Survey, Washington


People dying post catastrophe due to shaking
5
number
People dying post catastrophe due to shaking: source
EERI
People dying post catastrophe due to shaking: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.


People missing due to tsunami
0
number
People missing due to tsunami: source
EERI
People missing due to tsunami: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.

People killed due to tsunami
0
number
People killed due to tsunami: source
EERI
People killed due to tsunami: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.

People missing due to fire following
0
number
People missing due to fire following: source
EERI
People missing due to fire following: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.

People killed due to fire following
1
number
People killed due to fire following: source
USGS
People killed due to fire following: comment

Durkin, M. E., Thiel, C.C. and Schneider, J.E. (1994) "Casualties and Emergency Medical Response", in Loss Estimation and Procedures, The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response, Prof. Paper 1553-A, U.S. Geological Survey, Washington

People missing due to slope failures
0
number
People missing due to slope failures: source
USGS
People missing due to slope failures: comment

Durkin, M. E., Thiel, C.C. and Schneider, J.E. (1994) "Casualties and Emergency Medical Response", in Loss Estimation and Procedures, The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response, Prof. Paper 1553-A, U.S. Geological Survey, Washington

People killed due to slope failures
1
number
People killed due to slope failures: source
USGS
People killed due to slope failures: comment

Durkin, M. E., Thiel, C.C. and Schneider, J.E. (1994) "Casualties and Emergency Medical Response", in Loss Estimation and Procedures, The Loma Prieta, California, Earthquake of October 17, 1989: Societal Response, Prof. Paper 1553-A, U.S. Geological Survey, Washington

Loss: Building damage
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hide
Total number of buildings destroyed by shaking: status
N/A

Number of buildings damaged by shaking: status
N/A

Number of dwellings destroyed by shaking
11500
number
Number of dwellings destroyed by shaking: source
USGS
Number of dwellings destroyed by shaking: comment

Comerio, C. (1998) Housing Repair and Reconstruction After the Earthquake, in "Performance of the Built Environment", The Loma Prieta, California, Earthquake of October 17, 1989: Building Structures, Prof. Paper 1552-C, U.S. Geological Survey, Washington


Number of dwellings damaged by shaking
31600
number
Number of dwellings damaged by shaking: source
USGS
Number of dwellings damaged by shaking: comment

Comerio, C. (1998) Housing Repair and Reconstruction After the Earthquake, in "Performance of the Built Environment", The Loma Prieta, California, Earthquake of October 17, 1989: Building Structures, Prof. Paper 1552-C, U.S. Geological Survey, Washington


Loss: Socioeconomic
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hide
People homeless
10603
number
People homeless: source
EERI
People homeless: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.


Direct economic loss
5078
million US$
Direct economic loss: source
EERI
Direct economic loss: comment

Robert A. Olson, Shirley Mattingly, Charles Scawthorn, Jelena Pantelic, Dennis Mileti, Colleen Fitzpatrick, Steven Helmericks, C. Renwick Breck, Richard S. Olson, Kathleen Tierney, Richard Andrews, Paul Flores, Nicholas Jones, Eric Noji, and Frederick Krimgold (1990) SOCIOECONOMIC IMPACTS AND EMERGENCY RESPONSE. Earthquake Spectra: May 1990, Vol. 6, No. S1, pp. 393-431.



Insured loss
960
million US$
Insured loss: source
Munich Re

Demographics
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Total number of buildings: status
N/A