1898 Mare Island earthquake

1898 Mare Island earthquake
Carson City
Chico
Monterey
Origin time 07:43 March 31 UTC [1][2]
Magnitude 5.8–6.4 Mw [3]
Epicenter 38°12′N 122°24′W / 38.2°N 122.4°W / 38.2; -122.4Coordinates: 38°12′N 122°24′W / 38.2°N 122.4°W / 38.2; -122.4 [1][2]
Areas affected San Francisco Bay Area
Northern California
United States
Total damage $350,000 [1] – Moderate [2]
Max. intensity VIII (Severe) – IX (Violent) [4]
Tsunami Possible [5]

The 1898 Mare Island earthquake occurred in Northern California on March 30 at 23:43 local time with a moment magnitude of 5.8–6.4 and a maximum Mercalli intensity of VIII (Severe) – IX (Violent). With financial losses of $350,000, its area of perceptibility included much of northern and central California and western Nevada. Damage was the most pronounced on Mare Island, a peninsula in northern San Francisco Bay. While relatively strong effects there were attributed to vulnerable buildings, moderate effects elsewhere in the San Francisco Bay Area consisted of damaged or partially collapsed structures, and there were media reports of a small tsunami that followed.

Several independent investigations focused on different aspects to gain a better understanding of the intensity, magnitude, source fault, and epicenter of this pre-instrumental event. Most investigators placed it under or to the north of San Pablo Bay, though two earthquake catalogs gave specific coordinates that place it within the confines of the San Pablo Bay National Wildlife Refuge. One of the numerous strike-slip faults of the San Andreas Fault System in the North Bay are most often named as the source fault, but one seismologist's paper detailed how a dip-slip fault may have been responsible. Several more recent studies gave alternate perspectives that named specific faults as where the shock may have originated.

Tectonic setting

The San Andreas Fault SAF system is a network of right-lateral strike-slip faults that form a portion of a complex and diffuse plate boundary. The faults span on and off shore along the California portion of the Pacific Rim, and in the area near San Francisco Bay, the extent of the various fault strands are limited to about 80 kilometers (50 mi) wide from east to west. This system of faults terminates in the north at the Mendocino Triple Junction where the north-northwest trending SAF meets the east trending Mendocino Fracture Zone. It terminates in the south in a more gradual fashion at the Salton Sea where displacement transitions to a series of transform faults and spreading centers along the Gulf of California Rift Zone.[6]

Earthquake

The Rogers Creek Fault Zone
The Hayward Fault Zone
The Green Valley Fault

The shock was felt over an area of 120,000 km2, from Chico to Monterey, and to Carson City in western Nevada. Toppozada et al. 1992 compared the isoseismal map from the event to those of earthquakes that occurred during the instrumental period to resolve the magnitude. The intensity VI isoseismals for the 1969 Santa Rosa and 1984 Morgan Hill earthquakes were markedly smaller; only the 1989 Loma Prieta earthquake covered a larger area than that of the 1898 event. The isoseismals for intensity V, VII, and VIII were also compared for additional calibration, and 6.7 was presented as the magnitude of the event, which was presumed to have occurred on the southern Rogers Creek Fault. This estimate was later reduced to M6.4 in Toppozada & Branum 2002.[1][4][7]

Bakun 1999 also analyzed intensity details to resolve for magnitude and location, resulting in M6.3 and a location at the northeast end of San Pablo Bay. A technique called Bayesian inference was used by Wesson, Bakun, & Perkins 2003 showed that the northern Hayward Fault was the most likely source, with the Rogers Creek, southern Green Valley, Concord, and northern Green Valley faults as the next most likely. Media reports of a small non-destructive tsunami led Parsons et al. 2003 to conclude that a normal fault (rather than a strike-slip fault) may have been responsible for the shock. Another viewpoint from Hecker et al. 2005 was that the Rogers Creek Fault was not likely the source because their trench investigation showed that its most recent event had a maximum slip of 2 m (6 ft 7 in) and that the 1898 event was too small to result in that much displacement.[8]

Another seismologist re-examined the event following the 2014 South Napa earthquake and found that the heavy effects on Mare Island were a result of weak or deficient buildings. Comparing the intensity distribution of the two shocks revealed that it was indeed severe on Mare Island as it was likely close to the rupture, which may have involved both strands of the Franklin Fault (between the West Napa and Rogers Creek Faults). Although surface rupturing events have been documented on the Hayward–Rogers Creek Fault System just to the west, no surface rupture was associated with this earthquake. A magnitude range of 5.8–6.4 Mw was given, with the lower bound representing an average stress drop event and the higher bound for a lower stress drop event.[3]

Intensity

The isoseismal map from Toppozada & Real 1981 places the epicenter to the north of San Pablo Bay and shows elongated rings aligned NNW–SSE. The innermost intensity VIII (Severe) ring encompasses Vallejo, Mare Island, and much of San Pablo Bay, and also includes three instances of intensity IX (Violent), but the locations cannot be determined with accuracy due to a lack of map resolution. While San Francisco is within the intensity VII (Very strong) ring, Santa Cruz and San Jose are as marked intensity VI (Strong) exceptions within the intensity V (Moderate) ring. Ukiah, Stockton, Sacramento, and Gilroy also lay in the intensity V ring.[9]

Toppozada et al. 1992 presents an updated isoseimal map with slightly more conservative maximum intensities with specific locations and focuses on the near field rather than an extended perspective. The innermost isoseismal shows only one location that is an exception to intensity VIII. Tubbs Island, to the northwest of Mare Island, lists VIII–IX. Schellville, Lakeville, and Mare Island all show intensity VIII. A large number of locations are marked VI–VII, including Santa Rosa, San Rafael, Oakland, and San Francisco. No specific epicenter was given, and instead, it was acknowledged that it may have been anywhere within a broad area centered on the southern Rogers Creek Fault.[4]

Damage

While the National Geophysical Data Center categorizes the overall effects of the event as moderate, significant damage occurred at the Mare Island Naval Shipyard, where several buildings suffered partial or total collapse and some equipment was damaged. Other strong effects occurred at Vallejo and to the southeast in Benicia, where a cannery was damaged, and in Martinez where the courthouse was damaged. Other locations in Sonoma County that were severely affected included Schellville, Greenwood Estate, and near Petaluma Creek. The effects were less severe in San Francisco, but one building partially collapsed, a girls high school suffered damage valued at several thousand dollars, and soil conditions contributed to damage at the Whittier School.[1][10]

Tsunami

Numerous bay area newspapers reported on various disturbances that were experienced by mariners. In the Pacific Ocean, vessels southeast of Point Reyes and near the Farallon Islands reported feeling the shock, and a sharp rise in sea level was reported in the San Francisco Bay and on the Napa River. Upon examination of the event, tsunami experts declared that while the Rogers Creek Fault is primarily strike-slip, some vertical movement is possible, and a five-point scale (0–4) was used to certify whether a tsunami event had occurred. With 0 intended for "not a valid tsunami report" and 4 being "certainly a valid report", a score of 2 was assigned to the event, meaning that it was "possibly a valid report" based on insufficient information, nonexpert observations, and unclear descriptions.[5]

See also

References

  1. 1 2 3 4 5 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. 74, 112
  2. 1 2 3 National Geophysical Data Center / World Data Service (NGDC/WDS), Significant Earthquake Database, National Geophysical Data Center, NOAA, doi:10.7289/V5TD9V7K
  3. 1 2 Hough, S. E. (2014), Where was the 1898 Mare Island Earthquake? Insights from the 2014 South Napa Earthquake, Fall Meeting 2014, abstract #S44D-03, American Geolphysical Union, Bibcode:2014AGUFM.S44D..03H
  4. 1 2 3 Toppozada, T. R.; Bennett, J. H.; Hallstrom, C. L.; Youngs, L. G. (1992), "1898 "Mare Island" Earthquake at the Southern End of the Rodgers Creek Fault", Proceedings of The Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, Special Publication 113, California Department of Conservation, pp. 385–392
  5. 1 2 Lander, J. F.; Lockridge, P. A.; Kozuch, M. J. (1993), Tsunamis Affecting the West Coast of the United States 1806–1992 (PDF), NGDC Key to Geophysical Records Documentation No. 29, National Oceanic and Atmospheric Administration, pp. 11, 12, 19, 57, 58
  6. ↑ Wallace, R. E. (1990), "General features", The San Andreas Fault System, California – USGS Professional Paper 1515, United States Geological Survey, pp. 3–6, ISBN 978-0607716269
  7. ↑ Toppozada, T.; Branum, D. (2002), "California Earthquakes of M ≥ 5.5: Their History and the Areas Damaged", International Handbook of Earthquake & Engineering Seismology, Part A, Volume 81A (First ed.), Academic Press, p. 795, ISBN 978-0124406520
  8. ↑ Hecker, S.; Pantosti, D.; Schwartz, D. P.; Hamilton, J. C; Reidy, L. M.; Powers, T. J. (2005), "The most recent large earthquake on the Rodgers Creek fault, San Francisco Bay area", Bulletin of the Seismological Society of America, Seismological Society of America, 95 (3): 853, doi:10.1785/0120040134
  9. ↑ Toppozada, T. R.; Real, C. R. (1981), Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes (print), Open-File Report 81-262, United States Geological Survey, pp. 122, 167
  10. ↑ Perrine, C. D. (1899), Earthquakes in California in 1898, No. 161, United States Geological Survey, pp. 15–22
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