1987 Whittier Narrows earthquake
The 1987 Whittier Narrows earthquake occurred in the southern San Gabriel Valley and surrounding communities of southern California at 7,42 a. m. PDT on October 1. A large number of homes and businesses were impacted, along with roadway disruptions, mainly in Los Angeles, damage estimates ranged from $213–358 million, with 200 injuries, three directly-related deaths, and five additional fatalities that were associated with the event. Mercalli intensity values for the greater Los Angeles area varied with ranges from VI to VII, only Whittier experienced a level of VIII, the highest experienced during the event, with the historic uptown area suffering the greatest damage. A separate M5.2 strike-slip event occurred three days and several kilometers to the northwest that caused damage and one additional death. Beginning with the 1983 Coalinga earthquake, a blind thrust event in the central coast ranges of California, the October 1987 shock occurred on a previously unrecognized blind thrust fault that is now known as the Puente Hills thrust system.
The system is considered one of the faults in the United States due to its moderate dip. The main shock occurred near the border of the Puente Hills 3 kilometers north of the Whittier Narrows at a depth of 14 kilometers. First motion polarities, along with modelling of teleseismic P and S-waves, the shock was located adjacent to the west-northwest striking Whittier fault, which is primarily a strike-slip fault, but has a minor thrust component. Although most of the Los Angeles metropolitan area saw shaking in line with Mercalli Intensity values of VI or VII, Whittier experienced effects consistent with MMI values of VIII. The 7,42 a. m. shock was the strongest in the Los Angeles area since the 1971 San Fernando earthquake and was felt as far as San Diego and San Luis Obispo and Las Vegas, Nevada. Communication systems and local media were temporarily impaired and power was cut, other minor disruptions included a number of water and gas main breaks, shattered windows and some ceiling collapses.
Los Angeles County+USC Medical Center took a number of the injured, whose injuries were summarized by an emergency room spokesman as very bad to minor. While total casualties amounted to eight, the destruction of homes was significant, throughout Los Angeles and Ventura counties,123 homes and 1,347 apartments were destroyed, and an additional 513 homes and 2,040 apartments were damaged. An inspection of a bridge on Interstate 605 revealed that there were fractures on the support columns, which resulted in a temporary closure. Other typical failures included more than 1,000 gas leaks, with resulting in fire, ceramic elements on high-voltage substation equipment breaking. Caltech scientists recorded the events on a cluster of twelve strong motion sensors that were placed throughout the region with a total of 87 channels of recorded data. Nine of these instruments were located on the Caltech campus, two were at the nine story Jet Propulsion Laboratory building 180 and the device was placed on a hillside 5 km to the west.
Investigation of the accelerograms from these units revealed the strongest shaking lasted 4–5 seconds, the vertical accelerations were considered relatively high and early analysis indicated that the mainshock was complex, with a double train of P-waves arriving with a 1. 4–1.8 second interval
2003 San Simeon earthquake
The 2003 San Simeon earthquake occurred with a moment magnitude of 6.6 on the Central Coast of California, about 7 miles northeast of San Simeon. It occurred at 11,15 PST on December 22, the earthquake probably occurred on the Oceanic fault zone in the Santa Lucia Mountains. It was caused by thrust faulting and propagated southeast from the hypocenter for 12 miles, the most violent ground movement occurred within 50 miles of the epicenter, though the earthquake was felt as far away as Los Angeles. It was the most destructive earthquake to hit the U. S since the 1994 Northridge earthquake, the area where the quake struck displays complex faulting, between the Oceanic Fault and Nacimiento Fault zones, along with possible interaction from the Hosgri fault and San Simeon Fault zones. The area around the epicenter is sparsely populated and the most severe occurred in Paso Robles,24 miles east-southeast. The Acorn Building, a masonry building built in 1892, completely collapsed. Other unreinforced masonry buildings, some more than a century old, none of the buildings that had even partial retrofitting collapsed.
There was a wrongful death lawsuit filed by the relatives of the women against Mary Mastagni. The jury found Mastagni negligent in the care and maintenance of the Acorn Building, due to not retrofitting the building, two sulfur hot springs in Paso Robles erupted after the earthquake. One was underneath the lot of City Hall. Hot water and sediment were released at a rate of about 1,300 gallons per minute, there was formerly a bath house at the location and the spring was capped after it closed down. Another hot spring flowed out of the embankment at the Paso Robles Street exit on U. S. Route 101, outside of Paso Robles the damage was less severe, with unreinforced masonry buildings taking minor to moderate damage. Buildings even 40 miles from the epicenter in San Luis Obispo suffered minor damage such as ceiling tiles falling, brick veneers were disproportionately affected. In addition, water tanks in Paso Robles and Los Osos were damaged, residential buildings, predominantly one to two story wood frame structures, weathered the quake with little or no damage.
The damage that did occur was mostly limited to chimneys, although a house in Atascadero suffered severe damage when it moved off its foundation, the damage was probably caused by poor construction. There were fewer nails connecting the plywood siding to the sill than is required, the building that housed Atascaderos City Hall was damaged and vacated shortly after the quake. After extensive repairs, it reopened in August 2013, some wineries, especially those near the epicenter along State Route 46, reported damage such as barrels toppling and bursting. This earthquake damaged Mission San Miguel Arcángel, causing $15 million worth of damage, the earthquake caused extensive damage to George H. Flamson Middle School
2002 Denali earthquake
The 2002 Denali earthquake occurred at 22,12,41 UTC November 3 with an epicenter 66 km ESE of Denali National Park, United States. This 7.9 Mw earthquake was the largest recorded in the interior of the United States for more than 150 years, the shock was the strongest ever recorded in the interior of Alaska. Due to the location, there were no fatalities and only a few injuries. Due to the depth, it was felt at least as far away as Seattle. About 20 houseboats were damaged by a seiche on a lake in Washington State, the Denali-Totschunda fault is a major dextral strike-slip system, similar in scale to the San Andreas fault system. The Denali-Totschunda fault system is one of the structures that accommodate the accretion of the Yakutat terrane, on October 23,2002, there was a magnitude 6.7 earthquake located on the Denali fault. Because of its close to the November 3 event and the fact that it preceded it by only 11 days. The initial rupture on November 3 was on a thrust fault segment, the epicenter lies just 25 kilometers east of the October 23 foreshock.
The rupture jumped to the main Denali fault strand propagating for a further 220 km before jumping again onto the Totschunda fault, the total surface rupture was ca.340 km. There is evidence of local supershear propagation inferred from ground motions, minor damage was reported over a wide area but the only examples of severe damage were on highways that crossed the fault trace and areas that suffered liquefaction, e. g. Northway Airport. Several bridges were damaged but none so severely that they were closed to traffic, due to the general self-sufficiency of those living near the fault rupture, very few lifeline systems were compromised. These people tend to get water from wells, heat their homes and cook their meals with gas furnaces and stoves. The Trans-Alaska Pipeline System crosses the rupture trace, the pipeline suffered some damage to supports. There was no oil spillage, as the pipeline at that location was designed to move laterally along beams to withstand major movement on the Denali Fault, the pipeline was shut down for three days to allow for inspections but was reopened
Rocky Mountain Arsenal
The Rocky Mountain Arsenal was a United States chemical weapons manufacturing center located in the Denver Metropolitan Area in Commerce City, Colorado. The site was completed December 1942, operated by the United States Army throughout the 20th century and was controversial among local residents until its closure in 1992, much of the site is now protected as the Rocky Mountain Arsenal National Wildlife Refuge. It was helpful that the location was close to Stapleton airfield, in 1942, the US Army acquired 19,915 acres of land on which to manufacture weapons in support of World War II military activities at a cost of $62,415,000. Additionally, some of this land was used for a prisoner of war camp, a lateral was built off the High Line Canal to supply water to the Arsenal. Weapons manufactured at RMA included both conventional and chemical munitions, including phosphorus, mustard gas, lewisite. RMA is one of the few sites that had a stockpile of Sarin gas, the manufacture of these weapons continued until 1969.
Rocket fuel to support Air Force operations was manufactured and stored at RMA, through the 1970s until 1985, RMA was used as a demilitarization site to destroy munitions and chemically related items. Coinciding with these activities, from 1946 to 1982, the Army leased RMA facilities to private industries for the production of pesticides. One of the lessees, Shell Oil Company, along with Julius Hyman and Company and Colorado Fuel. The military reserved the right to oust these companies and restart chemical weapon production in the event of a national emergency, RMA contained a deep injection well that was constructed in 1961. It was drilled to a depth of 12,045 feet, the well was cased and sealed to a depth of 11,975 feet, with the remaining 70 feet left as an open hole for the injection of Basin F liquids. For testing purposes, the well was injected with approximately 568,000 US gallons of city water prior to injecting any waste. The injected fluids had very little potential for reaching the surface or usable groundwater supply since the point had 11,900 feet of rock above it and was sealed at the opening.
The Army discontinued use of the well in February 1966 because the fluid injection triggered a series of earthquakes in the area, the well remained unused until 1985 when the Army permanently sealed the disposal well. In 1987, the RMA was placed on the National Priorities List of Superfund sites, as provided by CERCLA, a Remedial Investigation/Feasibility Study was conducted to determine the extent of contamination. Since 1985, the mission at RMA has been the remediation of the site, ordnance was manufactured and tested, and asbestos and polychlorinated biphenyls were used at RMA. Today, it is considered a waste site according to the Colorado Department of Public. In 1986 it was discovered that the absence of activity had made the area an involuntary park when a winter communal roost of bald eagles
1925 Santa Barbara earthquake
The 1925 Santa Barbara earthquake hit the area of Santa Barbara, California on June 29, with a moment magnitude of 6.8 and a maximum Mercalli Intensity of IX. It resulted in 13 casualties and destroyed the center of the city. At 6,44 a. m. the mainshock occurred which lasted 19 seconds, the epicenter of the earthquake was located in the sea off the coast of Santa Barbara, in the Santa Barbara Channel. The fault on which it occurred appears to have been an extension of the Mesa fault or the Santa Ynez system, the earthquake was felt from Paso Robles to the north to Santa Ana to the south and to Mojave to the east. Major damage occurred in the city of Santa Barbara and along the coast, as well as north of Santa Ynez Mountains, including Santa Ynez and Santa Maria valleys. Though thirteen people died, it may have far worse without the actions of three, recognized heroes, who shut off the town gas and electricity preventing a possible catastrophic fire. Most homes survived the earthquake in relatively good shape, although nearly every chimney in the city crumbled, the downtown of Santa Barbara was destroyed, only a few buildings along State Street, the main commercial street in the city, were still standing after the earthquake.
The City Cab building and The Californian and Arlington garages, all large and fully occupied parking structures, collapsed full with cars of those traveling and on vacation. In the business district, an area of about 36 blocks, only a few structures were not substantially damaged, the facade of the church of the Mission Santa Barbara was severely damaged and lost its statues. Many important buildings, including hotels and the Potter Theater, were lost, the courthouse, library and churches were among the buildings sustaining serious damage. Concrete curbs buckled in almost every block in Santa Barbara, pavement on the boulevard along the beach was displaced by about 20–36 centimeters, but the pavement in the downtown generally was not damaged. The earthen Sheffield Dam had been close to the city in 1917. It was 720 feet long and 25 feet high and held 30 million US gallons of water. The soil under the dam liquefied during the earthquake and the dam collapsed, the Southern Pacific Company Railroad tracks were damaged in a number of places between Ventura and Gaviota, in particular, a portion between Naples and Santa Barbara was badly damaged and displaced.
Seaside bluffs fell into the ocean and a tsunami wave was noted by offshore ships. The town was cut off from telephone and telegraph, news from the outside world arrived by shortwave radio. The absence of post earthquake fire permitted scientists and geologists to study earthquake damage on various types of construction, additional fire and police personnel arrived from as far as Los Angeles to assist the sailors and soldiers in keeping the order. An aftershock on July 3 caused additional cracked walls and damaged chimneys and this development completely altered the character of the city center
2008 Chino Hills earthquake
The 2008 Chino Hills earthquake occurred at 11,42,15 a. m. PDT on July 29 in Southern California. The epicenter of the magnitude 5.5 earthquake was in Chino Hills, though no lives were lost, eight people were injured, and it caused considerable damage in numerous structures throughout the area and caused some amusement park facilities to shut down their rides. The earthquake led to increased discussion regarding the possibility of a earthquake in the future. The Chino Hills earthquake was caused by faulting, with components of both thrust and sinistral strike-slip displacement. Its epicenter was within 3 miles of Chino Hills and its hypocenter was c.9.1 miles deep. Initial estimations of the main shock reported it as magnitude 5.8. The main shock was felt as far south as San Diego, and Tijuana, Mexico. It was the strongest earthquake to occur in the greater Los Angeles area since the 1994 Northridge earthquake, there was an unusually low amount of seismic activity in Southern California in the week prior to the quake.
The Chino Hills earthquake caused no deaths or significant damage due to the location of its epicenter. Most of the infrastructure in the Chino Hills area is relatively new, the high volume of telephone use following the shock overloaded provider capacity and disrupted service into the afternoon. Amusement rides at Disneyland, Six Flags Magic Mountain, Universal Studios Hollywood and Knotts Berry Farm were evacuated, California State University, Fullerton suffered some damage in its older, inadequately engineered buildings. In Orange, the Chapman University School of Law was evacuated after a pipe was ruptured. Pipes on a Macys department store in Westfield Topanga ruptured during the flooding the store which closed for a couple of days in order to be repaired. A light fixture damaged by the shock started a fire in the Westfield MainPlace Mall in Santa Ana, since the fire was in an empty movie theater. A gap was reported on California State Route 91 near Anaheim Hills, c.7 miles southwest of the epicenter, a minor landslide near the freeway caused some traffic congestion, but structural damage were reported.
Caltrans replaced an expansion joint on an Interstate 5 truck overpass at the El Toro Y Interchange, the roof of Placentias public library nearly collapsed, the building was closed for repairs. Electrical outages were reported in Chino, Chino Hills, Diamond Bar, over 2,000 people lost power after a fire broke out at a La Habra power station, but electricity was restored that afternoon. Los Angeles International Airport reported a radar system outage along with a broken water heater
An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earths lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to people around. The seismicity or seismic activity of an area refers to the frequency, Earthquakes are measured using measurements from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe and these two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly imperceptible or weak and magnitude 7 and over potentially cause damage over larger areas. The largest earthquakes in historic times have been of magnitude slightly over 9, intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the damage to structures it causes. At the Earths surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground, when the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami.
Earthquakes can trigger landslides, and occasionally volcanic activity, in its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of faults, but by other events such as volcanic activity, mine blasts. An earthquakes point of rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter, tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior, once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface.
This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the portion of the fault. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface and this process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of a total energy is radiated as seismic energy. Most of the energy is used to power the earthquake fracture growth or is converted into heat generated by friction
1983 Coalinga earthquake
The 1983 Coalinga earthquake occurred on May 2 at exactly 23,42 UTC in Coalinga, California. The earthquake measured 6.2 on the moment magnitude scale and had a maximum Mercalli intensity of VIII, the earthquake was caused by an unknown fault buried under the surface. The shock was felt from the greater Los Angeles Area, north to Susanville in Lassen County, through July 31, more than 5,000 aftershocks were recorded, of which 894 had a magnitude of 2.5 or larger. Most of the larger magnitude shocks were felt in Coalinga, the Coalinga earthquake was caused by an 0. 5-meter uplift of the anticline ridge northeast of Coalinga, but surface faulting was not observed. About five weeks later, on June 11, however, an aftershock caused surface faulting about 12 km northwest of Coalinga and this earthquake caused an estimated $10 million in property damage and injured 94 people. Damage was most severe in Coalinga, where the 8-block downtown commercial district was almost completely destroyed, buildings having unreinforced brick walls sustained the heaviest damage.
Newer buildings, such as the Bank of America, the most significant damage outside the Coalinga area occurred at Avenal,31 kilometers southeast of the epicenter. Most public buildings, including the City Hall, schools, fire house, post office, only six bridges of 60 surveyed in the area sustained measurable structural damage. This damage consisted of hairline cracks and spalling at the top of the columns and displacement of wing walls and parapets. All public utilities were damaged to some degree, the water system continued to function despite many leaks in its transmission piping. Gas was shut off for days because of broken piping and leaks. One large section of old concrete sewer pipe west of the area partly collapsed. In the oil fields near Coalinga, surface facilities such as pumping units, storage tanks, one oil company administration building, about 7 km north of Coalinga, sustained major structural damage and its two brick chimneys were toppled. Subsurface damage, including collapsed or parted well casing, was observed only on 14 of 1,725 active wells and this earthquake triggered thousands of rockfalls and rockslides as far as 34 km northwest,15 km south, and 26 km southwest of the epicenter.
Only a few slope failures occurred east of the epicenter because of the absence of steep slopes in that direction, Coalinga recovered 98 percent of their expenses in repairing and rebuilding public buildings at a time when an 85 percent recovery rate was considered the standard success rate. In September 2006, the California Seismic Safety Commission was renamed the Alfred E. Alquist Seismic Safety Commission in honor of the recently deceased California politician Al Alquist. The Coalinga earthquake suggested to geologists that the State of California was in even worse condition than had been thought. The pace of activity along the Pacific coast was identified as a relevant subject for further study
1993 Scotts Mills earthquake
The 1993 Scotts Mills earthquake, known as the Spring break quake, occurred in the U. S. state of Oregon on March 25 at 5,34 AM Pacific Standard Time. Ground motion was widely felt in Oregons Willamette Valley, the Portland metropolitan area, the Scotts Mills mainshock epicenter was located about 5 kilometers east of the town of Scotts Mills in Marion County, and about 54 kilometers south of Portland. Reports of the came from as far as Roseburg in southern Oregon,165 miles south of the epicenter, to the coastal town of Lincoln City, east to Bend. The seismology lab from the University of Washington in Seattle reported the Richter magnitude to be 5.4, an aftershock measuring 3.2 happened within the first hour of the main shock. Most structural damage consisted of toppled chimneys and failure of walls of unreinforced masonry, buildings with damage include Molalla High School and the State Capitol in Salem. The damage at the capitol occurred in the old wing and that section of the facility was closed after the morning earthquake, additional damage to some homes occurred in Molalla in the form of broken windows and brick planters at some homes there.
No damage was reported in Portland, but residents did see books knocked off shelves, several people were treated at the Salem Hospital for injuries related to falling glass
1952 Kern County earthquake
The 1952 Kern County earthquake occurred on July 21 in the southern San Joaquin Valley and measured 7.3 on the moment magnitude scale. The main shock occurred at 4,52 am Pacific Daylight Time, killed 12 people and injured hundreds, a small sector of damage near Bealville corresponded to a maximum Mercalli intensity of XI, though this intensity rating was not representative of the majority of damage. The earthquake occurred on the White Wolf Fault near the community of Wheeler Ridge and was the strongest to occur in California since the 1906 San Francisco earthquake. The July mainshock had a significant aftershock sequence that persisted into July, ground disturbances that were created by the earthquakes were surveyed, both in the valley and in the foothills, with both vertical and horizontal displacements present in the epicentral area. At Lebec, just south of the epicenter of the July mainshock, the San Andreas Fault comes together with the Garlock Fault, the San Andreas has been responsible for considerable seismic activity at its northern and southern sections, and traverses the area near the Transverse Ranges.
The Owens Valley Fault, on the east side of the Sierran block, has been mapped, the 1952 earthquakes were the first to be observed well within Kern County lines. Other strong, but remote events were felt in the area. The county is bounded on the side by the Temblor Range which is adjacent to the southern San Andreas Fault. Other large events have affected the area as well, like the January 1857 Fort Tejon earthquake that severely affected Fort Tejon, the M7.3 earthquake occurred on the strike-slip White Wolf Fault in the southern San Joaqin Valley. Historically, the fault has had a component of reverse slip. The epicenter of the shock was at the 90 km faults southwestern end, at a point where it may end, the White Wolf Fault was found to be curved, with less dip on the northeast end, though that zone had a higher strike-slip component. Other distinct characteristics on that end of the fault were the shallower shocks, if the total fault displacement came about as a result of the same type of large-displacement shocks like the one in 1952, the recurrence interval was proposed to be 170–450 years.
The 1995 Working Group on California Earthquake Probabilities gave a slip rate estimate of 2 mm per year.5 meters, because of the extraordinary damage there, an intensity rating of XI was assigned specifically for that location. Though damage was spread throughout an area, most was concentrated in the town of Tehachapi where at least 11 were killed and 35 were injured. An early estimate reported in the Los Angeles Times had the damage at $2.6 million with 700 families affected in Tehachapi alone, fifteen homes were destroyed there,53 were heavily damaged, and another 75 sustained light damage. In Bakersfield, windows were broken and dislodged plaster littered residential and commercial districts, to the southwest of Bakersfield in Maricopa, the justice court building, the Maricopa Hotel, the post office, and several businesses were condemned because of heavy damage. In the small town of Taft disruption was light, with the exception of a wall at a J. C. Penney department store. Power disruptions affected Van Nuys and Los Angeles and in Long Beach some windows were broken, other moderate damage in that area included a 2.5 ft crack on a street in Hollywood and a 90 ft crack in a Santa Ana parking lot
1989 Loma Prieta earthquake
The 1989 Loma Prieta earthquake occurred in Northern California on October 17 at 5,04 p. m. local time. With a moment magnitude of 6.9 and a maximum Mercalli intensity of IX, no surface faulting occurred, though a large number of other ground failures and landslides were present, especially in the Summit area of the Santa Cruz Mountains. Due to the coverage of the 1989 World Series, it became the first major earthquake in the United States that was broadcast live on national television. Andrew Lawson, a geologist from the University of California, had named the fault after the San Andreas Lake and led an investigation into that event. The San Andreas Fault ruptured for a length of 290 mi during the 1906 shock, several long term forecasts for a large shock along the San Andreas Fault in that area had been made public prior to 1989 but the earthquake that transpired was not what had been anticipated. The 1989 Loma Prieta event originated on an undiscovered oblique-slip reverse fault that is located adjacent to the San Andreas Fault, since many forecasts had been presented for the region near Loma Prieta, seismologists were not taken by surprise by the October 1989 event.
Two moderate shocks, referred to as the Lake Elsman earthquakes by the USGS, occurred in the Santa Cruz Mountains region in June 1988, each events aftershock sequence and effect on stress drop was closely examined, and their study indicated that the shocks affected the mainshocks rupture process. The June 27,1988, shock occurred with an intensity of VI. Its effects included broken windows in Los Gatos, and other damage in Holy City. Farther away from the Santa Cruz Mountains, pieces of concrete fell from a structure at the Sunnyvale Town Center. More moderate damage resulted from the August 8,1989, shock when chimneys were toppled in Cupertino, Los Gatos, other damage included cracked walls and foundations and broken underground pipes. At the office of the Los Gatos City Manager, a window that was cracked had broken in the earlier shock. Also in Los Gatos, one man died when he exited a building through a window, the Loma Prieta earthquake was named for Loma Prieta Peak in the Santa Cruz Mountains, which lies just to the east of the mainshock epicenter.
At sites with rocky terrain, the duration was shorter and the shaking was much less intense, the strong motion records allowed for the causative fault to be determined – the rupture was related to the San Andreas Fault System. While a Mercalli Intensity of VIII covered a large swath of territory relatively close to the further to the north. At more than 44 miles distant, the San Francisco Bay Area recorded peak horizontal accelerations that were as high as 0. 26g, in a general way, the location of aftershocks of the event delineated the extent of the faulting, which extended about 24 miles in length. Because the rupture took place bilaterally, the duration of strong shaking was about half of what it would have been had it ruptured in one direction only, the duration of a typical M6.9 shock with a comparable rupture length would have been about twice as long. Gregory Beroza, a seismologist with Stanford University, made several distinctions regarding the 1906 and 1989 events, near Loma Prieta, the 1906 rupture was more shallow, had more strike-slip, and occurred on a fault that was near vertical