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William H. Bakun

Publications and source records attributed to William H. Bakun.

11 recordsLinked to original sources
USGS2013

Assessing the location and magnitude of the 20 October 1870 Charlevoix, Quebec, earthquake

The Charlevoix, Quebec, earthquake of 20 October 1870 caused damage to several towns in Quebec and was felt throughout much of southeastern Canada and along the U.S. Atlantic seaboard from Maine to Maryland. Site‐specific damage and felt reports from Canadian and U.S. cities and towns were used in analyses of the location and magnitude of the earthquake. The macroseismic center of the earthquake was very close to Baie‐St‐Paul, where the greatest damage was reported, and the intensity magnitude M I was found to be 5.8, with a 95% probability range of 5.5–6.0. After corrections for epicentral‐distance differences are applied, the modified Mercalli intensity (MMI) data for the 1870 earthquake and for the moment magnitude M 6.2 Charlevoix earthquake of 1925 at common sites show that on average, the MMI readings are about 0.8 intensity units smaller for the 1870 earthquake than for the 1925 earthquake, suggesting that the 1870 earthquake was M I 5.7. A similar comparison of the MMI data for the 1870 earthquake with the corresponding data for the M 5.9 1988 Saguenay event suggests that the 1870 earthquake was M I 6.0. These analyses all suggest that the magnitude of the 1870 Charlevoix earthquake is between M I 5.5 and M I 6.0, with a best estimate of M I 5.8.

Bulletin of the Seismological Society of America↗
USGS2012

Significant earthquakes on the Enriquillo fault system, Hispaniola, 1500-2010: Implications for seismic hazard

Historical records indicate frequent seismic activity along the north-east Caribbean plate boundary over the past 500 years, particularly on the island of Hispaniola. We use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 Haiti earthquakes to derive an intensity attenuation relation for Hispaniola. The intensity assignments and the attenuation relation are used in a grid search to find source locations and magnitudes that best fit the intensity assignments. Here we describe a sequence of devastating earthquakes on the Enriquillo fault system in the eighteenth century. An intensity magnitude M I 6.6 earthquake in 1701 occurred near the location of the 2010 Haiti earthquake, and the accounts of the shaking in the 1701 earthquake are similar to those of the 2010 earthquake. A series of large earthquakes migrating from east to west started with the 18 October 1751 M I 7.4–7.5 earthquake, probably located near the eastern end of the fault in the Dominican Republic, followed by the 21 November 1751 M I 6.6 earthquake near Port-au-Prince, Haiti, and the 3 June 1770 M I 7.5 earthquake west of the 2010 earthquake rupture. The 2010 Haiti earthquake may mark the beginning of a new cycle of large earthquakes on the Enriquillo fault system after 240 years of seismic quiescence. The entire Enriquillo fault system appears to be seismically active; Haiti and the Dominican Republic should prepare for future devastating earthquakes.

Hispaniola↗
USGS2012

Accounts of damage from historical earthquakes in the northeastern Caribbean to aid in the determination of their location and intensity magnitudes

Earthquakes have been documented in the northeastern Caribbean since the arrival of Columbus to the Americas; written accounts of these felt earthquakes exist in various parts of the world. To better understand the earthquake cycle in the Caribbean, the records of earthquakes in earlier catalogs and historical documents from various archives, which are now available online, were critically examined. This report updates previous catalogs of earthquakes, in particular earthquakes in Hispaniola, to give to the public the most comprehensive documentation of earthquake damage and to further the understanding of the earthquake cycle in the northeastern Caribbean. Documentation of an event in the past depended on the population and political trends of the island, and the availability of historical documents is limited by the physical resource digitization schedule and by the copyright laws of each archive. Examples of documents accessed are governors' letters, newspapers, and other circulars published within the Caribbean, North America, and Western Europe. Key words were used to search for publications that contain eyewitness accounts of various large earthquakes. Finally, this catalog provides descriptions of damage to buildings used in previous studies for the estimation of moment intensity (MI) and location of significantly damaging or felt earthquakes in Hispaniola and in the northeastern Caribbean, all of which have been described in other studies.

Open-File Report↗
USGS2011

Pay a little now, or a lot later

Odds are 2-in-3 that at least one disastrous earthquake will strike the San Francisco Bay Area before 2020. Faced with this threat, corporations and government agencies have stepped up efforts that will reduce future losses by billions of dollars.

Fact Sheet↗
USGS2010

The 2007 M5.4 Alum Rock, California, earthquake: Implications for future earthquakes on the central and southern Calaveras Fault

[1] The similarity of seismograms recorded by two seismic stations demonstrate that the 31 October 2007 moment magnitude M 5.4 Alum Rock earthquake is a repeat of a 1955 M L 5.5 earthquake. Both occurred on Oppenheimer et al.'s (1990) Zone V “stuck patch” on the central Calaveras fault, providing new support for their model of Calaveras fault earthquake activity. We suggest that Zone V fails only in a family of recurring M ∼ 5.4–5.5 earthquakes. The 1955 and 2007 earthquakes are the penultimate and ultimate Zone V events. Earthquakes in 1891 and 1864 are possible earlier Zone V events. The next Zone V event is not expected in the next few decades, assuming a time‐dependent recurrence model: the mean forecast date is 2064 (2035–2104, 95% confidence range). We further suggest that Zones I, II, III, and IV fail in recurring M ∼ 5.1–5.3, M ∼ 5.6–5.8, M ∼ 6.1–6.3, and M ∼ 4.9–5.0 earthquakes, respectively. If our earthquake recurrence model is correct, the next Zone I event is overdue and could occur anytime, and M 5–6 earthquakes should not occur on Zones II, III, and IV before 2014, 2012, and 2026, respectively. We cannot rule out the possibility that Zone VI, which lies at the southern end of the Mission Seismic Trend, where the southern Hayward and central Calaveras faults appear to connect at depth, fails aseismically or in large events on the southern Hayward fault, such as last occurred in 1868, or in large events on the adjoining northern Calaveras fault segment.

California↗
USGS2010

Locations and magnitudes of historical earthquakes in the Sierra of Ecuador (1587–1996)

The whole territory of Ecuador is exposed to seismic hazard. Great earthquakes can occur in the subduction zone (e.g. Esmeraldas, 1906, M w 8.8), whereas lower magnitude but shallower and potentially more destructive earthquakes can occur in the highlands. This study focuses on the historical crustal earthquakes of the Andean Cordillera. Several large cities are located in the Interandean Valley, among them Quito, the capital (∼2.5 millions inhabitants). A total population of ∼6 millions inhabitants currently live in the highlands, raising the seismic risk. At present, precise instrumental data for the Ecuadorian territory is not available for periods earlier than 1990 (beginning date of the revised instrumental Ecuadorian seismic catalogue); therefore historical data are of utmost importance for assessing seismic hazard. In this study, the Bakun & Wentworth method is applied in order to determine magnitudes, locations, and associated uncertainties for historical earthquakes of the Sierra over the period 1587–1976. An intensity-magnitude equation is derived from the four most reliable instrumental earthquakes ( M w between 5.3 and 7.1). Intensity data available per historical earthquake vary between 10 (Quito, 1587, Intensity ≥VI) and 117 (Riobamba, 1797, Intensity ≥III). The bootstrap resampling technique is coupled to the B&W method for deriving geographical confidence contours for the intensity centre depending on the data set of each earthquake, as well as confidence intervals for the magnitude. The extension of the area delineating the intensity centre location at the 67 per cent confidence level (±1σ) depends on the amount of intensity data, on their internal coherence, on the number of intensity degrees available, and on their spatial distribution. Special attention is dedicated to the few earthquakes described by intensities reaching IX, X and XI degrees. Twenty-five events are studied, and nineteen new epicentral locations are obtained, yielding equivalent moment magnitudes between 5.0 and 7.6. Large earthquakes seem to be related to strike slip faults between the North Andean Block and stable South America to the east, while moderate earthquakes ( M w ≤ 6) seem to be associated with to thrust faults located on the western internal slopes of the Interandean Valley.

Geophysical Journal International↗
USGS2008

Historical seismicity in the South San Francisco Bay Region

Locations (intensity centers) and moment magnitude M for 24 earthquakes (1858-1911) in the southern San Francisco Bay area are estimated from Modified Mercalli intensity (MMI) assignments. The uncertainties in location and M are generally large because there are few MMI assignments available. Preferred locations are selected to be consistent with a simple model for seismic activity on the central and southern Calaveras fault. Significant seismic activity can be explained by repetitive failure of the same fault areas in nearly identical earthquakes. Significant earthquake activity occurred on both east- and west-Bay faults in the ten or so years before the 1868 east-Bay earthquake and before the1906 and 1989 west-Bay earthquakes.

Open-File Report↗
USGS1998

Modified Mercalli intensities for some recent California earthquakes and historic San Francisco Bay Region earthquakes

Modified Mercalli Intensity ( MMI ) data for recent California earthquakes were used by Bakun and Wentworth (1997) to develop a strategy for bounding the location and moment magnitude M of earthquakes from MMI observations only. Bakun ( Bull. Seismol. Soc. Amer. , submitted) used the Bakun and Wentworth (1997) strategy to analyze 19 th century and early 20 th century San Francisco Bay Region earthquakes. The MMI data and site corrections used in these studies are listed in this Open-file Report.

California↗