1980 Eureka earthquake: Difference between revisions

1980 Eureka earthquake
	Salem Riley Lake City Fallon Chowchilla
UTC time	1980-11-08 10:27:34
ISC event	635132
USGS-ANSS	ComCat
Local date	November 8, 1980
Local time	02:27:34 PST
Magnitude	7.3 Mw
Depth	6.2 mi (10 km)
Epicenter	41°08′N 124°26′W / 41.13°N 124.44°W
Type	Strike-slip
Areas affected	North Coast (California) ; United States
Total damage	$2–2.75 million
Max. intensity	MMI VII (Very strong)
Peak acceleration	0.15–0.25 g
Landslides	Yes
Casualties	Six injured

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The 1980 Eureka earthquake (also known as the Gorda Basin earthquake) occurred on November 8 at 02:27:34 local time along the northern coastal area of California in the United States. With a moment magnitude of 7.3 and a maximum Mercalli intensity of VII (Very strong), this strike-slip earthquake was the largest to occur in California in 28 years. Although damage was considered light, several loss estimates equaled or exceeded $2 million, and six injuries resulted when two vehicles came down with the partial collapse of a highway overpass on US 101 in Fields Landing. The north coast of California experiences frequent plate boundary earthquakes near the Mendocino triple junction and intraplate events also occur within the Gorda plate.

Due to the regional seismic risk, the nuclear portion of the Humboldt Bay Nuclear Power Plant was shut down in the 1970s. No substantial damage occurred to the two fossil-fuel units that were still operational at the facility. Several types of sensors were installed at the site to capture strong motion data in this seismically active area, but the majority of records from the event were considered unreliable due to faulty equipment or inadequate maintenance. Only one piece of equipment at the facility provided data by which an estimate of the peak ground acceleration could be made.

Tectonic setting

Near Cape Mendocino, the Mendocino triple junction is an area of active seismicity where three tectonic plates come together. The Mendocino fracture zone (also known as the Mendocino Fault east of the Gorda Ridge) is a transform fault that separates the Pacific and Gorda plates. To the south, the relative motion between the Pacific plate and North American plate is accommodated by the San Andreas Fault, and to the north, the Gorda plate is converging with the North American plate at the Cascadia subduction zone. Earthquakes within the Gorda plate are the result of north–south compression at the Mendocino Fault.^[5]

Earthquake

The left-lateral strike-slip earthquake was the largest to occur in California since the 1952 Kern County earthquake. The mainshock (which was described as a multiple-rupture, with four subevents in the initial 80 seconds) and its aftershocks occurred on a northeast-trending fault that extended from near the Mendocino Fault to a point northwest of Eureka. Movement along the fault is due to a north–south compressional regime and the resulting intraplate deformation of the Gorda plate. Previous events in this area were the January 1922 7.3 M_s and the January 1923 7.2 M_s  shocks.^[6]

The earthquake occurred offshore (to the northwest of Eureka, about 37 mi (60 km) west of Patrick's Point) and had a maximum Mercalli intensity of VII (Very strong). Some people reported intense shaking that lasted for 15 to 30 seconds. In the epicentral area, items were knocked off shelves and furniture was displaced, but damage was considered light (the smaller 5.2 M_L event that occurred in June 1975 caused more damage).^[7]

Damage

While most of the damage from the Gorda Basin earthquake was considered light, there were some exceptions. In Eureka, effects included broken windows and dishes, fallen chimneys, and merchandise that fell from store shelves. In Fields Landing, King Salmon, Loleta, and Big Lagoon areas, the strongest effects included surface cracks on the ground, soil liquefaction, small landslides and rockfalls, and numerous slumps along the Eel River. Similar effects occurred along the Old Coast Highway near Trinidad and Moonstone, where the roadway was reduced to one lane of travel in some areas. Several homes were knocked off their foundations and a highway overpass collapsed in Fields Landing. Seismic wave amplification, poor design, or inadequate construction style may have contributed to losses there.^[7]^[8]

Tompkins Hill Road overpass

The Tompkins Hill Road overpass is situated just south of Fields Landing and was built in the late 1960s. It suffered slight damage during the 1975 earthquake and was due for a retrofit in 1981. The overpass was constructed with cement abutments on earthen ramps on either end and a series of concrete support columns in the middle. Eight 60 ft (20 m) reinforced concrete spans accommodated northbound and southbound lanes of traffic, with no anchors connecting the spans with each other or to the abutments. At the time of the shock, two of the southbound spans came off their support (a 6 in (15 cm) ledge) and six people were injured when a Volkswagen Beetle and a small pickup truck plummeted off the bridge.^[7]

MMI	Locations
Selected Mercalli intensities
MMI VII (Very strong)	Fields Landing
MMI VI (Strong)	Brookings, Eureka
MMI V (Moderate)	Crescent City, Scotia
MMI IV (Light)	Fallon, Roseburg
MMI III (Weak)	Lake City, Chowchilla
MMI II (Weak)	Eugene
Stover & von Hake 1984, pp. 55–59

Humboldt Bay Power Plant

The Humboldt Bay Power Plant is located about 3 miles (4.8 km) north of the collapsed highway overpass and operated fossil-fuel and nuclear units in the 1960s and 1970s. The nuclear unit was cancelled in 1976 because of seismic safety concerns, but the two fossil-fuel units remained in operation. The Nuclear Regulatory Commission performed a post-event survey of the facility's systems in late 1980, but inspectors found only minor effects to the plant's structure, piping, tanks, and other mechanical equipment. It was found that the two units were automatically shut down at the time of the shock for various protective concerns and that there were minor cracks in masonry and concrete, sheared bolts, pipe leaks, and slight movement of water tanks. The deformation of a reinforced masonry wall that resulted in a variable-width gap was the only structural issue.^[4]

Intensity

With an area of perceptibility of more than 97,000 mi², it was felt from the San Francisco Bay Area and the Central Valley to western Nevada, and as far as Salem in northern Oregon. Intensity VI (Strong) effects were limited to a narrow coastal zone that included Myers Flat in the south and Brookings, Oregon in the north. Damage at this intensity level included broken plate glass windows, cracked walls, foundation and chimney damage, and significant loss of merchandise. In Fields Landing, two homes that came off their foundations, the fallen overpass, and broken gas, water, and sewer lines were associated with intensity VII (Very strong) shaking.^[9]

Strong motion

Pacific Gas and Electric initially reported that peak ground accelerations in the range of 0.16–0.4 g were recorded on the floor of the refueling building on the plant's strong motion instruments (accelerometers). Low voltage from a faulty power supply left the instruments in a condition that was functional, but the records were not considered reliable. Three TERA Technology film recorders were also in use as a backup system, but these instruments also did not produce any usable records, because lack of maintenance had allowed dirt and grit to get inside. Only records from one instrument (an Engdhal peak shock recorder) was believed to be operating correctly, and with a close examination of the energy dispersed at various frequencies, an estimate of 0.15–0.25 g was given for the event at that location.^[4]

References

^ ^a ^b ^c ISC (2015), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 2.0, International Seismological Centre
^ ^a ^b PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey, September 4, 2009
^ ^a ^b ^c Stover, C. W.; Coffman, J. L. (1993), Seismicity of the United States, 1568–1989 (Revised) – U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, pp. 95, 168
^ ^a ^b ^c Herring, K. S; Rooney, V.; Chokshi, N. C. (1981), Reconnaissance report : effects of November 8, 1980 earthquake on Humboldt Bay Power Plant and Eureka, California area, U.S. Nuclear Regulatory Commission, pp. 1–8, archived from the original on 2016-03-05, retrieved 2015-08-03
^ Bakun, W. H. (2000), "Seismicity of California's North Coast", Bulletin of the Seismological Society of America, 90 (4): 797–812, Bibcode:2000BuSSA..90..797B, doi:10.1785/0119990138
^ Lay, T.; Given, J. W.; Kanamori, H. (1982), "Long-period mechanism of the 8 November 1980 Eureka, California, earthquake", Bulletin of the Seismological Society of America, 72 (2): 439, 440, 455, 456, Bibcode:1982BuSSA..72..439L, doi:10.1785/BSSA0720020439
^ ^a ^b ^c Lajoie, K.; Keefer, D. (1981), "Investigations of the 8 November 1980 earthquake in Humboldt County, California", Open-File Report, Open-File Report 81-397, United States Geological Survey, pp. 1, 4, 8, 9, 12–16, doi:10.3133/ofr81397
^ Kilbourne, R. T.; Saucedo, G. J. (1981), "Gorda Basin Earthquake, Northwestern California", California Geology, 34 (3): 53–57, archived from the original on 2016-02-07, retrieved 2015-08-03
^ Stover, C. W.; von Hake, C. A. (1984), "United States earthquakes, 1980", Open-File Report, Open-File Report 84-980, pp. 55–59, Bibcode:1982use..rept.....S, doi:10.3133/ofr84980

External links

M7.2 – offshore Northern California – United States Geological Survey
When the bridge fell: Father looks back on 30th anniversary of quake that claimed overpass – Times-Standard
A Quake, a Collapse and No Responsibility – The New York Times
IE Circular No. 81-03, Inoperable Seismic Monitoring Instrumentation – U.S. Nuclear Regulatory Commission
The International Seismological Centre has a bibliography and/or authoritative data for this event.

[ISC-GEM-1] ISC (2015), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 2.0, International Seismological Centre

[PAGER-CAT-2] PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey, September 4, 2009

[Stover-3] Stover, C. W.; Coffman, J. L. (1993), Seismicity of the United States, 1568–1989 (Revised) – U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, pp. 95, 168

[nrc-4] Herring, K. S; Rooney, V.; Chokshi, N. C. (1981), Reconnaissance report : effects of November 8, 1980 earthquake on Humboldt Bay Power Plant and Eureka, California area, U.S. Nuclear Regulatory Commission, pp. 1–8, archived from the original on 2016-03-05, retrieved 2015-08-03

[Bakun-5] Bakun, W. H. (2000), "Seismicity of California's North Coast", Bulletin of the Seismological Society of America, 90 (4): 797–812, Bibcode:2000BuSSA..90..797B, doi:10.1785/0119990138

[6] Lay, T.; Given, J. W.; Kanamori, H. (1982), "Long-period mechanism of the 8 November 1980 Eureka, California, earthquake", Bulletin of the Seismological Society of America, 72 (2): 439, 440, 455, 456, Bibcode:1982BuSSA..72..439L, doi:10.1785/BSSA0720020439

[Lajoie-7] Lajoie, K.; Keefer, D. (1981), "Investigations of the 8 November 1980 earthquake in Humboldt County, California", Open-File Report, Open-File Report 81-397, United States Geological Survey, pp. 1, 4, 8, 9, 12–16, doi:10.3133/ofr81397

[cg-8] Kilbourne, R. T.; Saucedo, G. J. (1981), "Gorda Basin Earthquake, Northwestern California", California Geology, 34 (3): 53–57, archived from the original on 2016-02-07, retrieved 2015-08-03

[9] Stover, C. W.; von Hake, C. A. (1984), "United States earthquakes, 1980", Open-File Report, Open-File Report 84-980, pp. 55–59, Bibcode:1982use..rept.....S, doi:10.3133/ofr84980

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@@ Line 1: / Line 1: @@
+{{Short description|Along the northern coastal area of California}}
 {{Infobox earthquake
  | name        = 1980 Eureka earthquake
@@ Line 19: / Line 20: @@
  | local-date  = {{Start date|1980|11|08}}
  | local-time  = 02:27:34 PST
- | magnitude   = 7.3 {{M|w|link=y}} <ref name=ISC-GEM/>
+ | magnitude   = 7.3 {{M|w|link=y}}<ref name=ISC-GEM/>
- | depth       = {{convert|10|km|abbr=on|order=flip}} <ref name=ISC-GEM/>
+ | depth       = {{convert|10|km|abbr=on|order=flip}}<ref name=ISC-GEM/>
- | location    = {{coord|41.13|-124.44|region:US_type:event|display=inline,title}} <ref name=ISC-GEM/>
+ | location    = {{coord|41.13|-124.44|region:US_type:event|display=inline,title}}<ref name=ISC-GEM/>
- | type        = [[Fault (geology)#Strike-slip faults|Strike-slip]] <ref name=PAGER-CAT/>
+ | type        = [[Fault (geology)#Strike-slip faults|Strike-slip]]<ref name=PAGER-CAT/>
  | affected    = [[North Coast (California)]] <br> United States
- | damage     = $2–2.75 million <ref name=PAGER-CAT/><ref name=Stover/>
+ | damage     = $2–2.75 million<ref name=PAGER-CAT/><ref name=Stover/>
- | intensity   = [[Mercalli intensity scale|VII (''Very strong'')]] <ref name=Stover/>
+ | intensity   = {{MMI|VII}}<ref name=Stover/>
- | pga         = .15–.25''[[Peak ground acceleration|g]]'' <ref name=nrc/>
+ | pga         = 0.15–0.25 ''[[Peak ground acceleration|g]]''<ref name=nrc/>
  | landslide   = Yes
- | casualties  = Six injured <ref name=Stover/>
+ | casualties  = Six injured<ref name=Stover/>
 }}
-The '''1980 Eureka earthquake''' (also known as the '''Gorda Basin earthquake''') occurred on November 8 at {{tooltip|02:27:34 local time|10:27:34 UTC}} along the northern coastal area of [[California]] in the [[United States]]. With a [[moment magnitude scale|moment magnitude]] of 7.3 and a maximum [[Mercalli intensity scale|Mercalli intensity]] of VII (''Very strong''), this [[Fault (geology)#Strike-slip faults|strike-slip]] earthquake was the largest to occur in California in 28 years. Although damage was considered light, several loss estimates equaled or exceeded $2 million, and six injuries resulted when two vehicles came down with the partial collapse of a highway overpass on [[U.S. Route 101 in California|US 101]] in [[Fields Landing, California|Fields Landing]]. The north coast of California experiences frequent [[Plate tectonics|plate boundary]] earthquakes near the [[Mendocino Triple Junction]] and [[intraplate earthquake|intraplate events]] also occur within the [[Gorda Plate]].
+The '''1980 Eureka earthquake''' (also known as the '''Gorda Basin earthquake''') occurred on November 8 at {{tooltip|02:27:34 local time|10:27:34 UTC}} along the northern coastal area of [[California]] in the United States. With a [[moment magnitude scale|moment magnitude]] of 7.3 and a maximum [[Mercalli intensity scale|Mercalli intensity]] of VII (''Very strong''), this [[Fault (geology)#Strike-slip faults|strike-slip]] earthquake was the largest to occur in California in 28 years. Although damage was considered light, several loss estimates equaled or exceeded $2 million, and six injuries resulted when two vehicles came down with the partial collapse of a highway overpass on [[U.S. Route 101 in California|US 101]] in [[Fields Landing, California|Fields Landing]]. The north coast of California experiences frequent [[Plate tectonics|plate boundary]] earthquakes near the [[Mendocino triple junction]] and [[intraplate earthquake|intraplate events]] also occur within the [[Gorda plate]].
-Due to the regional [[seismic risk]], the nuclear portion of the [[Humboldt Bay Nuclear Power Plant]] was shut down in the 1970s. No substantial damage occurred to the two [[Fossil-fuel power station|fossil-fuel]] units that were still operational at the facility. Several types of sensors were installed at the site to capture strong motion data in this seismically-active area, but the majority of records from the event were considered unreliable due to faulty equipment or inadequate maintenance. Only one piece of equipment at the facility provided data by which an estimate of the [[peak ground acceleration]] could be made.
+Due to the regional [[seismic risk]], the nuclear portion of the [[Humboldt Bay Nuclear Power Plant]] was shut down in the 1970s. No substantial damage occurred to the two [[Fossil-fuel power station|fossil-fuel]] units that were still operational at the facility. Several types of sensors were installed at the site to capture strong motion data in this seismically active area, but the majority of records from the event were considered unreliable due to faulty equipment or inadequate maintenance. Only one piece of equipment at the facility provided data by which an estimate of the [[peak ground acceleration]] could be made.
 ==Tectonic setting==
 {{See also|Convergent boundary|Mid-ocean ridge}}
-Near [[Cape Mendocino]], the Mendocino Triple Junction is an area of active seismicity where three tectonic plates come together. The [[Mendocino Fracture Zone]] (also known as the Mendocino Fault east of the [[Gorda Ridge]]) is a [[transform fault]] that separates the [[Pacific Plate|Pacific]] and [[Gorda Plate]]s. To the south, the relative motion between the Pacific Plate and [[North American Plate]] is accommodated by the [[San Andreas Fault]], and to the north, the Gorda Plate is converging with the North American Plate at the [[Cascadia Subduction Zone]]. Earthquakes within the Gorda Plate are the result of north–south compression at the Mendocino Fault.<ref name=Bakun>{{citation|title=Seismicity of California's North Coast|url=http://bssa.geoscienceworld.org/content/90/4/797.abstract|first=W. H.|last=Bakun|year=2000|journal=Bulletin of the Seismological Society of America|volume=90|number=4|pages=797–812|bibcode=2000BuSSA..90..797B|doi=10.1785/0119990138}}</ref>
+Near [[Cape Mendocino]], the Mendocino triple junction is an area of active seismicity where three tectonic plates come together. The [[Mendocino fracture zone]] (also known as the Mendocino Fault east of the [[Gorda Ridge]]) is a [[transform fault]] that separates the [[Pacific plate|Pacific]] and [[Gorda plate]]s. To the south, the relative motion between the Pacific plate and [[North American plate]] is accommodated by the [[San Andreas Fault]], and to the north, the Gorda plate is converging with the North American plate at the [[Cascadia subduction zone]]. Earthquakes within the Gorda plate are the result of north–south compression at the Mendocino Fault.<ref name=Bakun>{{citation|title=Seismicity of California's North Coast|url=http://bssa.geoscienceworld.org/content/90/4/797.abstract|first=W. H.|last=Bakun|year=2000|journal=Bulletin of the Seismological Society of America|volume=90|number=4|pages=797–812|bibcode=2000BuSSA..90..797B|doi=10.1785/0119990138}}</ref>
 ==Earthquake==
@@ Line 44: / Line 45: @@
 {{See also|Strike-slip tectonics}}
-The [[Sinistral and dextral|left-lateral]] strike-slip earthquake was the largest to occur in California since the [[1952 Kern County earthquake]]. The mainshock (which was described as a multiple-rupture, with four subevents in the initial 80 seconds) and its aftershocks occurred on a northeast-trending [[Fault (geology)|fault]] that extended from near the Mendocino Fault to a point northwest of [[Eureka, California|Eureka]]. Movement along the fault is due to a north–south compressional regime and the resulting [[intraplate deformation]] of the Gorda Plate. Previous events in this area were the January 1922 7.3 {{M|s|link=y}} and the January 1923 7.2 {{M|s}} shocks.<ref>{{citation|title=Long-period mechanism of the 8 November 1980 Eureka, California, earthquake|url=http://www.bssaonline.org/content/72/2/439.abstract|first=T.|last=Lay|first2=J. W.|last2=Given|first3=H.|last3=Kanamori|author-link3=Hiroo Kanamori|year=1982|journal=Bulletin of the Seismological Society of America|volume=72|number=2|pages=439, 440, 455, 456}}</ref>
+The [[Sinistral and dextral|left-lateral]] strike-slip earthquake was the largest to occur in California since the [[1952 Kern County earthquake]]. The mainshock (which was described as a multiple-rupture, with four subevents in the initial 80 seconds) and its aftershocks occurred on a northeast-trending [[Fault (geology)|fault]] that extended from near the Mendocino Fault to a point northwest of [[Eureka, California|Eureka]]. Movement along the fault is due to a north–south compressional regime and the resulting [[intraplate deformation]] of the Gorda plate. Previous events in this area were the January 1922 7.3 {{M|s|link=y}} and the January 1923 7.2 {{M|s}} shocks.<ref>{{citation|title=Long-period mechanism of the 8 November 1980 Eureka, California, earthquake|url=https://authors.library.caltech.edu/48513/|first1=T.|last1=Lay|first2=J. W.|last2=Given|first3=H.|last3=Kanamori|author-link3=Hiroo Kanamori|year=1982|journal=Bulletin of the Seismological Society of America|volume=72|number=2|pages=439, 440, 455, 456|doi=10.1785/BSSA0720020439|bibcode=1982BuSSA..72..439L}}</ref>
-The earthquake occurred offshore (to the northwest of Eureka, about {{convert|60|km|abbr=on|order=flip}} west of Patrick's Point) and had a maximum Mercalli intensity of VII (''Very strong''). Some people reported intense shaking that lasted for 15 to 30 seconds. In the epicentral area, items were knocked off shelves and furniture was displaced, but damage was considered light (the smaller 5.2 {{M|l|link=y}} event that occurred in June 1975 caused more damage).<ref name=Lajoie>{{citation|title=Investigations of the 8 November 1980 earthquake in Humboldt County, California|url=https://pubs.er.usgs.gov/publication/ofr81397|first=K.|last=Lajoie|first2=D.|last2=Keefer|year=1981|publisher=[[United States Geological Survey]]|series=Open-File Report 81-397|pp=1, 4, 8, 9, 12–16}}</ref>
+The earthquake occurred offshore (to the northwest of Eureka, about {{convert|60|km|abbr=on|order=flip}} west of Patrick's Point) and had a maximum Mercalli intensity of VII (''Very strong''). Some people reported intense shaking that lasted for 15 to 30 seconds. In the epicentral area, items were knocked off shelves and furniture was displaced, but damage was considered light (the smaller 5.2 {{M|l|link=y}} event that occurred in June 1975 caused more damage).<ref name=Lajoie>{{citation|chapter=Investigations of the 8 November 1980 earthquake in Humboldt County, California|chapter-url=https://pubs.er.usgs.gov/publication/ofr81397|first1=K.|last1=Lajoie|first2=D.|last2=Keefer|title=Open-File Report|year=1981|publisher=United States Geological Survey|series=Open-File Report 81-397|pages=1, 4, 8, 9, 12–16|doi=10.3133/ofr81397|doi-access=free}}</ref>
 ===Damage===
-While most of the damage from the Gorda Basin earthquake was considered light, there were some exceptions. In Eureka, effects included broken windows and dishes, fallen chimneys, and merchandise that fell from store shelves. In Fields Landing, King Salmon, Loleta, and Big Lagoon areas, the strongest effects included surface cracks on the ground, [[soil liquefaction]], small landslides and [[rockfall]]s, and numerous [[Slump (geology)|slumps]] along the [[Eel River (California)|Eel River]]. Similar effects occurred along the Old Coast Highway near [[Trinidad, California|Trinidad]] and [[Moonstone, California|Moonstone]], where the roadway was reduced to one lane of travel in some areas. Several homes were knocked off their foundations and a highway overpass collapsed in Fields Landing. [[Seismic wave]] amplification, poor design, or inadequate construction style may have contributed to losses there.<ref name=Lajoie/><ref name=cg>{{citation|title=Gorda Basin Earthquake, Northwestern California|url=http://www.johnmartin.com/earthquakes/eqpapers/00000050.htm|first=R. T.|last=Kilbourne|first2=G. J.|last2=Saucedo|year=1981|journal=California Geology|volume=34|number=3|pages=53–57}}</ref>
+While most of the damage from the Gorda Basin earthquake was considered light, there were some exceptions. In Eureka, effects included broken windows and dishes, fallen chimneys, and merchandise that fell from store shelves. In Fields Landing, King Salmon, Loleta, and Big Lagoon areas, the strongest effects included surface cracks on the ground, [[soil liquefaction]], small landslides and [[rockfall]]s, and numerous [[Slump (geology)|slumps]] along the [[Eel River (California)|Eel River]]. Similar effects occurred along the Old Coast Highway near [[Trinidad, California|Trinidad]] and [[Moonstone, California|Moonstone]], where the roadway was reduced to one lane of travel in some areas. Several homes were knocked off their foundations and a highway overpass collapsed in Fields Landing. [[Seismic wave]] amplification, poor design, or inadequate construction style may have contributed to losses there.<ref name=Lajoie/><ref name=cg>{{citation|title=Gorda Basin Earthquake, Northwestern California|url=http://www.johnmartin.com/earthquakes/eqpapers/00000050.htm|first1=R. T.|last1=Kilbourne|first2=G. J.|last2=Saucedo|year=1981|journal=California Geology|volume=34|number=3|pages=53–57|access-date=2015-08-03|archive-date=2016-02-07|archive-url=https://web.archive.org/web/20160207191157/http://www.johnmartin.com/earthquakes/eqpapers/00000050.htm|url-status=dead}}</ref>
 ====Tompkins Hill Road overpass====
@@ Line 62: / Line 63: @@
 ! [[Mercalli intensity scale|MMI]] !! Locations
 |-
+| {{MMI|VII}}
-| VII (''Very strong'')
 | [[Fields Landing, California|Fields Landing]]
 |-
+| {{MMI|VI}}
-| VI (''Strong'')
 | [[Brookings, Oregon|Brookings]], [[Eureka, California|Eureka]]
 |-
+| {{MMI|5}}
-| V (''Moderate'')
 | [[Crescent City, California|Crescent City]], [[Scotia, California|Scotia]]
 |-
+| {{MMI|IV}}
-| IV (''Light'')
 | [[Fallon, Nevada|Fallon]], [[Roseburg, Oregon|Roseburg]]
 |-
-| III (''Weak'')
+| {{MMI|III}}
 | [[Lake City, Modoc County, California|Lake City]], [[Chowchilla, California|Chowchilla]]
 |-
+| {{MMI|II}}
-| II (''Weak'')
 | [[Eugene, Oregon|Eugene]]
 |-
@@ Line 86: / Line 87: @@
 {{Main|Humboldt Bay Nuclear Power Plant}}
-The Humboldt Bay Power Plant is located about {{convert|3|mi|sp=us}} north of the collapsed highway overpass and operated [[Fossil-fuel power station|fossil-fuel]] and nuclear units in the 1960s and 1970s. The nuclear unit was cancelled in 1976 because of seismic safety concerns, but the two fossil-fuel units remained in operation. The [[Nuclear Regulatory Commission]] performed a post-event survey of the facility's systems in late 1980, but inspectors found only minor effects to the plant's structure, piping, tanks, and other mechanical equipment. It was found that the two units were automatically shut down at the time of the shock for various protective concerns and that there were minor cracks in masonry and concrete, sheared bolts, pipe leaks, and slight movement of water tanks. The deformation of a reinforced masonry wall that resulted in a variable-width gap was the only structural issue.<ref name=nrc>{{citation|title=Reconnaissance report : effects of November 8, 1980 earthquake on Humboldt Bay Power Plant and Eureka, California area|url=http://nisee.berkeley.edu/elibrary/Text/S22158|first=K. S|last=Herring|first2=V.|last2=Rooney|first3=N. C.|last3=Chokshi|year=1981|publisher=[[Nuclear Regulatory Commission|U.S. Nuclear Regulatory Commission]]|pages=1–8|access-date=2015-08-03|archive-url=https://web.archive.org/web/20160305010730/http://nisee.berkeley.edu/elibrary/Text/S22158|archive-date=2016-03-05|url-status=dead}}</ref>
+The Humboldt Bay Power Plant is located about {{convert|3|mi|sp=us}} north of the collapsed highway overpass and operated [[Fossil-fuel power station|fossil-fuel]] and nuclear units in the 1960s and 1970s. The nuclear unit was cancelled in 1976 because of seismic safety concerns, but the two fossil-fuel units remained in operation. The [[Nuclear Regulatory Commission]] performed a post-event survey of the facility's systems in late 1980, but inspectors found only minor effects to the plant's structure, piping, tanks, and other mechanical equipment. It was found that the two units were automatically shut down at the time of the shock for various protective concerns and that there were minor cracks in masonry and concrete, sheared bolts, pipe leaks, and slight movement of water tanks. The deformation of a reinforced masonry wall that resulted in a variable-width gap was the only structural issue.<ref name=nrc>{{citation|title=Reconnaissance report : effects of November 8, 1980 earthquake on Humboldt Bay Power Plant and Eureka, California area|url=http://nisee.berkeley.edu/elibrary/Text/S22158|first1=K. S|last1=Herring|first2=V.|last2=Rooney|first3=N. C.|last3=Chokshi|year=1981|publisher=[[Nuclear Regulatory Commission|U.S. Nuclear Regulatory Commission]]|pages=1–8|access-date=2015-08-03|archive-url=https://web.archive.org/web/20160305010730/http://nisee.berkeley.edu/elibrary/Text/S22158|archive-date=2016-03-05|url-status=dead}}</ref>
 ===Intensity===
-With an area of perceptibility of more than 97,000&nbsp;mi<sup>2</sup>, it was felt from the [[San Francisco Bay Area]] and the [[Central Valley (California)|Central Valley]] to [[western Nevada]], and as far as [[Salem, Oregon|Salem]] in northern Oregon. Intensity VI (''Strong'') effects were limited to a narrow coastal zone that included [[Myers Flat, California|Myers Flat]] in the south and [[Brookings, Oregon]] in the north. Damage at this intensity level included broken plate glass windows, cracked walls, foundation and chimney damage, and significant loss of merchandise. In Fields Landing, two homes that came off their foundations, the fallen overpass, and broken gas, water, and sewer lines were associated with intensity VII (''Very strong'') shaking.<ref>{{citation|title=United States earthquakes, 1980|url=https://pubs.er.usgs.gov/publication/ofr84980|first=C. W.|last=Stover|first2=C. A.|last2=von Hake|year=1984|series=Open-File Report 84-980|pages=55–59|bibcode=1982use..rept.....S}}</ref>
+With an area of perceptibility of more than 97,000&nbsp;mi<sup>2</sup>, it was felt from the [[San Francisco Bay Area]] and the [[Central Valley (California)|Central Valley]] to [[western Nevada]], and as far as [[Salem, Oregon|Salem]] in northern Oregon. Intensity VI (''Strong'') effects were limited to a narrow coastal zone that included [[Myers Flat, California|Myers Flat]] in the south and [[Brookings, Oregon]] in the north. Damage at this intensity level included broken plate glass windows, cracked walls, foundation and chimney damage, and significant loss of merchandise. In Fields Landing, two homes that came off their foundations, the fallen overpass, and broken gas, water, and sewer lines were associated with intensity VII (''Very strong'') shaking.<ref>{{citation|chapter=United States earthquakes, 1980|chapter-url=https://pubs.er.usgs.gov/publication/ofr84980|first1=C. W.|last1=Stover|first2=C. A.|last2=von Hake|title=Open-File Report|year=1984|series=Open-File Report 84-980|pages=55–59|doi=10.3133/ofr84980|bibcode=1982use..rept.....S|doi-access=free}}</ref>
 ===Strong motion===
 {{see also|Strong ground motion}}
-[[Pacific Gas and Electric Company|Pacific Gas and Electric]] initially reported that [[peak ground acceleration]]s in the range of .16–.4''[[Peak ground acceleration|g]]'' were recorded on the floor of the refueling building on the plant's strong motion instruments ([[accelerometer]]s). Low voltage from a faulty power supply left the instruments in a condition that was functional, but the records were not considered reliable. Three TERA Technology film recorders were also in use as a backup system, but these instruments also did not produce any usable records, because lack of maintenance had allowed dirt and grit to get inside. Only records from one instrument (an Engdhal peak shock recorder) was believed to be operating correctly, and with a close examination of the energy dispersed at various frequencies, an estimate of .15–.25''[[Peak ground acceleration|g]]'' was given for the event at that location.<ref name=nrc/>
+[[Pacific Gas and Electric Company|Pacific Gas and Electric]] initially reported that peak ground accelerations in the range of 0.16–0.4 ''g'' were recorded on the floor of the refueling building on the plant's strong motion instruments ([[accelerometer]]s). Low voltage from a faulty power supply left the instruments in a condition that was functional, but the records were not considered reliable. Three TERA Technology film recorders were also in use as a backup system, but these instruments also did not produce any usable records, because lack of maintenance had allowed dirt and grit to get inside. Only records from one instrument (an Engdhal peak shock recorder) was believed to be operating correctly, and with a close examination of the energy dispersed at various frequencies, an estimate of 0.15–0.25 ''g'' was given for the event at that location.<ref name=nrc/>
+==See also==
+{{Portal|California}}
+*[[List of earthquakes in 1980]]
+*[[List of earthquakes in California]]
 ==References==
-{{reflist|30em|refs=
+{{reflist|refs=
 <ref name=ISC-GEM>{{citation|title=ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009)|url=http://www.isc.ac.uk/iscgem/index.php|author=ISC|year=2015|publisher=[[International Seismological Centre]]|series=Version 2.0}}</ref>
-<ref name=PAGER-CAT>{{citation|title=PAGER-CAT Earthquake Catalog|url=https://earthquake.usgs.gov/enwiki/static/lfs/data/pager/catalogs/|author=USGS|date=September 4, 2009|publisher=[[United States Geological Survey]]|series=Version 2008_06.1}}</ref>
+<ref name=PAGER-CAT>{{citation|title=PAGER-CAT Earthquake Catalog|url=https://earthquake.usgs.gov/enwiki/static/lfs/data/pager/catalogs/|date=September 4, 2009|publisher=United States Geological Survey|series=Version 2008_06.1}}</ref>
 <ref name=Stover>{{citation|last1=Stover|first1=C. W.|last2=Coffman|first2=J. L.|title=Seismicity of the United States, 1568–1989 (Revised) – U.S. Geological Survey Professional Paper 1527|url=https://books.google.com/books?id=bY0KAQAAIAAJ|year=1993|publisher=[[United States Government Printing Office]]|pages=95, 168}}</ref>
 }}
 ==External links==
-* [https://earthquake.usgs.gov/earthquakes/eventpage/usp0001aq1#general_summary M7.2 – offshore Northern California] – [[United States Geological Survey]]
+* [https://earthquake.usgs.gov/earthquakes/eventpage/usp0001aq1#general_summary M7.2 – offshore Northern California] – United States Geological Survey
 * [http://www.times-standard.com/20101108/when-the-bridge-fell-father-looks-back-on-30th-anniversary-of-quake-that-claimed-overpass When the bridge fell: Father looks back on 30th anniversary of quake that claimed overpass] – ''[[Times-Standard]]''
 * [https://www.nytimes.com/2010/11/19/us/19bcjames.html?_r=0 A Quake, a Collapse and No Responsibility] – ''[[The New York Times]]''
-* [https://www.nrc.gov/reading-rm/doc-collections/gen-comm/circulars/1981/cr81003.html IE Circular No. 81-03, Inoperable Seismic Monitoring Instrumentation] – [[Nuclear Regulatory Commission|U.S. Nuclear Regulatory Commission]]
+* [https://www.nrc.gov/reading-rm/doc-collections/gen-comm/circulars/1981/cr81003.html IE Circular No. 81-03, Inoperable Seismic Monitoring Instrumentation] – U.S. Nuclear Regulatory Commission
 * {{EQ-isc-link|635132}}
@@ Line 118: / Line 124: @@
 [[Category:Earthquakes in California]]
 [[Category:History of Humboldt County, California]]
+[[Category:1980 in California]]
+[[Category:Eureka, California]]
+[[Category:Strike-slip earthquakes]]

v t e Earthquakes in California
Very Large (7.0–7.9)	1812 San Juan Capistrano (6.9–7.5) 1812 Ventura (7.1–7.5) 1838 San Andreas (6.8–7.2) 1857 Fort Tejon (7.9) 1872 Owens Valley (7.4–7.9) 1892 Laguna Salada (7.1–7.2) 1906 San Francisco (7.8) 1915 Baja California (7.0) 1927 Lompoc (7.3) 1952 Kern County (7.3) 1980 Eureka (7.3) 1992 Cape Mendocino (7.2) 1992 Landers (7.3) 1999 Hector Mine (7.1) 2010 Baja California (7.2) 2019 Ridgecrest (7.1) 2024 Cape Mendocino (7.0)
Large (6.0–6.9)	1868 Hayward (6.3–6.7) 1892 Vacaville–Winters (6.4, 6.2) 1898 Mare Island (5.8–6.4) 1899 San Jacinto (6.7) 1915 Imperial Valley (6.3 & 6.3) 1918 San Jacinto (6.7) 1925 Santa Barbara (6.8) 1932 Eureka (6.4) 1933 Long Beach (6.4) 1940 El Centro (6.9) 1948 Desert Hot Springs (6.4) 1954 Eureka (6.5) 1968 Borrego Mountain (6.6) 1971 San Fernando (6.5–6.7) 1979 Imperial Valley (6.4) 1983 Coalinga (6.2) 1984 Morgan Hill (6.2) 1986 North Palm Springs (6.0) 1986 Chalfant Valley (6.2) 1987 Superstition Hills (6.2, 6.6) 1989 Loma Prieta (6.9) 1992 Joshua Tree (6.2) 1992 Big Bear (6.5) 1994 Northridge (6.7) 2003 San Simeon (6.6) 2010 Eureka (6.5) 2014 South Napa (6.0) 2019 Ridgecrest (6.4) 2022 Ferndale (6.4)
Moderate (5.0–5.9)	1957 San Francisco (5.7) 1969 Santa Rosa (5.6, 5.7) 1973 Point Mugu (5.8) 1979 Coyote Lake (5.7) 1980 Livermore (5.8) 1981 Westmorland (5.9) 1987 Whittier Narrows (5.9) 1990 Upland (5.7) 1991 Sierra Madre (5.6) 2000 Yountville (5.0) 2007 Alum Rock (5.6) 2008 Chino Hills (5.4) 2014 La Habra (5.1)

v t e Earthquakes in the United States
Historical	1585 Aleutian Islands 1638 New Hampshire 1663 Charlevoix 1700 Cascadia 1755 Cape Ann 1783 New Jersey 1811–12 New Madrid 1812 San Juan Capistrano 1812 Santa Barbara 1838 San Andreas 1857 Fort Tejon 1865 Memphis 1867 Manhattan, Kansas 1868 Hawaii 1868 Hayward 1870 Charlevoix 1871 Lānaʻi 1872 Owens Valley 1872 North Cascades 1882 Fort Collins 1886 Charleston 1887 Sonora 1892 Laguna Salada 1892 Vacaville–Winters 1895 Charleston 1898 Mare Island 1899 San Jacinto
20th century	1901 Richfield 1906 San Francisco 1906 Aleutian Islands 1909 Wabash River 1914 Reno 1915 Imperial Valley 1915 Pleasant Valley 1916 Irondale 1918 San Jacinto 1921 Sevier Valley 1925 Montana 1925 Santa Barbara 1927 Lompoc 1931 Valentine 1932 Eureka 1932 Cedar Mountain 1933 Long Beach 1934 Hansel Valley 1935 Helena 1936 State Line 1940 El Centro 1940 New Hampshire 1944 Cornwall–Massena 1946 Aleutian Islands 1947 Wisconsin 1948 Desert Hot Springs 1949 Olympia 1952 Kern County 1954 Churchill County 1957 Andreanof Islands 1957 San Francisco 1958 Huslia 1958 Lituya Bay 1959 Hebgen Lake 1962 Cache Valley 1964 Alaska 1965 Rat Islands 1965 Puget Sound 1968 Borrego Mountain 1968 Illinois 1969 Santa Rosa 1971 San Fernando 1973 Point Mugu 1975 Near Islands 1975 Morris 1975 Hawaii 1979 Coyote Lake 1979 Imperial Valley 1980 Eureka 1981 Westmorland 1983 Coalinga 1983 Borah Peak 1983 Kaoiki 1984 Morgan Hill 1986 North Palm Springs 1986 Chalfant Valley 1987 Whittier Narrows 1987 Imperial Valley 1989 Loma Prieta 1990 Upland 1991 Sierra Madre 1992 Joshua Tree 1992 Cape Mendocino 1992 Landers 1992 Big Bear 1992 St. George 1993 Scotts Mills 1993 Klamath Falls 1994 Northridge 1995 Marathon 1998 Pymatuning 1999 Hector Mine 2000 Yountville
21st century	2001 Nisqually 2002 Denali 2003 Alabama 2003 San Simeon 2006 Gulf of Mexico 2006 Kiholo Bay 2008 Illinois 2008 Chino Hills 2008 Reno 2008 Wells 2010 Eureka 2010 Baja California 2011 Colorado 2011 Virginia 2011 Oklahoma 2013 Port Alexander 2014 La Habra 2014 Aleutian Islands 2014 Southeast Alaska 2014 South Napa 2016 Oklahoma 2018 Alaska 2018 Hawaii 2018 Anchorage 2018 Southern Appalachian 2019 Ridgecrest 2020 Salt Lake City 2020 Central Idaho 2020 Monte Cristo Range 2020 Sparta 2021 Chignik 2022 Ferndale 2023 Texas 2024 New Jersey 2024 Cape Mendocino
Swarms	2001 Enola 2008 Reno 2010–11 Guy–Greenbrier 2012 Brawley 2009–present Oklahoma 2019 Ridgecrest

v t e ← Earthquakes in 1980 →
Azores Islands (6.9, Jan 1)† Livermore (5.8, Jan 24) Nepal (6.5, Jul 29)† Mammoth Lakes (6.2, May 25) Honduras (6.4, Aug 9) El Asnam (7.1, Oct 10)†‡ Oaxaca (7.2, Oct 24)† Eureka (7.3, Nov 8) Irpinia (6.9, Nov 23)†
† indicates earthquake resulting in at least 30 deaths ‡ indicates the deadliest earthquake of the year