1838 San Andreas earthquake

1838 San Andreas earthquake
San Francisco
Monterey
Local date June 1838 (1838-06)
Magnitude 6.8–7.2 Mw [1]
Epicenter 37°18′N 122°09′W / 37.30°N 122.15°W / 37.30; -122.15Coordinates: 37°18′N 122°09′W / 37.30°N 122.15°W / 37.30; -122.15 (approximate)[2]
Areas affected San Francisco Bay Area
Northern California
United States
Max. intensity VIII (Severe) [3]
Casualties Unknown

The 1838 San Andreas earthquake is believed to be a rupture along the northern part of the San Andreas Fault in June 1838.[1][4] It affected approximately 100 km (62 miles) of the fault, from the San Francisco Peninsula to the Santa Cruz Mountains.[1] It was a strong earthquake, with an estimated moment magnitude of 6.8 to 7.2,[1] making it one of the largest known earthquakes in California. The region was lightly populated at the time, although structural damage was reported in San Francisco, Oakland, and Monterey.[1][5][6] It is unknown whether there were fatalities. Based on geological sampling, the fault created approximately 1.5 meters (5.0 feet) of slip.[1]

For years, another large earthquake was said to have occurred two years earlier on June 10, 1836 along the Hayward fault,[7] however this is now believed to be referring to the 1838 San Andreas earthquake.[8] There is no evidence a large earthquake hit the region in 1836.[8]

History of Faulting incidents

Earthquake ruptures along Hayward fault and San Andreas Fault

Not to be mistaken, the Hayward fault 1836 earthquake was speculated to have the similar effects of the San Andreas Fault earthquake. The Hayward Fault was reported in the affected cities: Santa Clara, and the East of San Francisco Bay.[8] Prior to 1838 and the inception of 1776 Mission San Francisco Dolores, there had been no reported evidence of earthquakes. The post-1600 earthquake ruptures along several faults were depicted by records of the infrastructure in missions damaged, which were historically significant for evaluating evidence of earthquakes in the San Francisco Bay Area. [4] The previous stress fractures were inferred in 1650-1770, while the M <7 was between 1776 and 1836.[9] The speculation of the 1836 earthquake occurring at the North Hayward area were small shocks. The eruption of the Hayward fault in 1868 derived from the stress concentrated in the Hayward fault during the 1838.[9]

Reports of experienced earthquakes

In June 1838, ground rupture probably occurred on the San Andreas fault at least from near Lone Mountain, south of San Francisco, toward Mission Santa Clara.[8]The earthquake was destructive in the East Bay at San Leandro and Mission San Jose. The faulting was narrated as a greater intensity than the 1906 earthquake, due to its damages to redwood trees and large extent aftershocks felt in Oakland and Monterrey. Due to the numerous widely felt aftershocks, the rupture along Hayward fault was probably influenced by the San Andreas fault earthquake[8] and not indicative of being 1836, as no reported damage was indicated by people living near Oakland. While memoirs evidently appeared in the newspaper following the 1868 Hayward earthquake, the 1838 earthquake was narrated as a more destructive earthquake than the 1868 earthquake.

Sightings of earthquake destruction of East Bay were described partially in the Sonoma Democrat, 14 October 1865 article: It was unquestionably the most severe that has been experienced since the advent of Americans here, but not comparable to the one which occurred about the year 1838, which shook down thick-walled adobe houses, and caused mountainsides to slide down. At that time the adobe house of Estudillo, an old settler in Alameda County, was thrown down and a large portion of a mountainside, near San Leandro, gave way and slid down to its base. The place where the slide occurred is plainly visible from the town of San Leandro. But the shaking up we received, last Sunday [8th], was quite sufficient to satisfy the present inhabitants. The amount of damage must be very large, though it will probably never be known. Besides a number of buildings which were ruined [in San Francisco], there are a great many others badly cracked and otherwise injured.[8]

Intensity Earthquake

The 1838 San Andreas earthquake was a fault rupture that extended from San Francisco to San Juan Bautista. Since the South Francisco Bay is at the center of three plate boundary fault zones, many occurrences of earthquakes of magnitude <7 were recorded. The intensity of the earthquake had magnitude 7 ½ and extended to the Hayward fault. There is evidence of the fault rupture extending to Monterey because the aftershocks reached San Juan Bautista and Oakland. The rupture extending to San Francisco to San Juan Bautista had a length totaling ∼ 140 km and indicating an M ∼ 7:4 earthquake. [1] It also caused two large aftershocks in 1840 and 1841. Toppozada and Borchardt (1998) compile damage reports of the extent of faulting in this event, as reported by Louderback (1947), and report strong intensities in Woodside, where solid adobe houses were cracked severely and redwoods were “broken off and hurled.”[1] Its damaging effects are due to its proximity to the several faults along the San Andreas Fault. Paleoseismic suggest that the June 1838 earthquake had a Mercalli intensity XI and that its rupture was along the San Francisco Peninsula, but it did not go past the Santa Cruz Mountains to the extent of the Grizzly Flat area.[10]Even though studies have measured stress patterns comparing the deformation along fault segments, there is no precise location to the total extent of these earthquake ruptures. North of Grizzly Flat was detected to experience a 7.1 magnitude and there was not a surface slip, despite it being on the San Andreas Fault.[9] The strike-slip ranged from Magnitude ~6.8- ~7.5 as evidence maps its inconsistent stress patterns distributing out from the Santa Francisco Bay Area.

See also

References

  1. 1 2 3 4 5 6 7 8 Streig, A. R.; Dawson, T. E.; Weldon II, R. J. (2014), "Paleoseismic Evidence of the 1890 and 1838 Earthquakes on the Santa Cruz Mountains Section of the San Andreas Fault, near Corralitos, California", Bulletin of the Seismological Society of America, Seismological Society of America, 104 (1): 285–300, Bibcode:2014BuSSA.104..285S, doi:10.1785/0120130009
  2. ↑ "Anniversaries of Notable California Earthquakes". California Geological Survey. Retrieved 24 October 2016.
  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, p. 72
  4. 1 2 Schwartz, D. P.; Lienkaemper, J. J.; Hecker, S.; Kelson, K. I.; Fumal, T. E.; Baldwin, J. N.; Seitz, G. G.; Niemi, T. M. (2014), "The Earthquake Cycle in the San Francisco Bay Region: A.D. 1600–2012" (PDF), Bulletin of the Seismological Society of America, Seismological Society of America, 104 (3): 1299–1328, Bibcode:2014BuSSA.104.1299S, doi:10.1785/0120120322
  5. ↑ Kovach, Robert L. (2004). Early Earthquakes of the Americas. Cambridge University Press. p. 148.
  6. ↑ "Historic Earthquakes". U.S. Geological Survey.
  7. ↑ Coffman, Jerry L.; von Hake, Carl A. Earthquake History of the United States (PDF). National Oceanic and Atmospheric Administration. p. 138.
  8. 1 2 3 4 5 6 Toppozada, T. R.; Borchardt, G. (1998), "Re-evaluation of the 1836 "Hayward fault" and the 1838 San Andreas fault earthquakes", Bulletin of the Seismological Society of America, Seismological Society of America, 88 (1): 140–159
  9. 1 2 3 Pollitz, F., Bakun, W., & Nyst, M. (2004). A physical model for strain accumulation in the San Francisco Bay region: Stress evolution since 1838. Journal of Geophysical Research: Solid Earth, 109(B11)
  10. ↑ Paleoseismic studies of the San Francisco Peninsula segment of the San Andreas Fault zone near Woodside, California. (1999). Journal of Geophysical Research: Solid Earth, 104(B10), 23,231
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