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The 1857 Fort Tejon earthquake, characterized by an estimated moment magnitude of 7.9, primarily impacted central and Southern California.
Answer: True
The source states that the 1857 Fort Tejon earthquake had an estimated moment magnitude of 7.9 and primarily occurred in central and Southern California.
The actual epicenter of the 1857 Fort Tejon earthquake was situated at Fort Tejon, which is the reason for its nomenclature.
Answer: False
The earthquake is named after Fort Tejon because it was the location of the greatest observed damage, not its actual epicenter, which was near Parkfield, California.
The 1857 Fort Tejon earthquake ruptured the northern segment of the San Andreas Fault for approximately 225 miles between San Francisco and Sacramento.
Answer: False
The 1857 earthquake ruptured the southern part of the San Andreas Fault for about 225 miles (350 km) between Parkfield and Wrightwood, not the northern part between San Francisco and Sacramento.
The maximum perceived intensity of the 1857 Fort Tejon earthquake was rated as IX (Violent) on the Modified Mercalli Intensity scale, with this intensity being felt near Fort Tejon.
Answer: True
The source confirms that the maximum perceived intensity of the 1857 Fort Tejon earthquake was IX (Violent) on the Modified Mercalli Intensity scale, felt near Fort Tejon and along the San Andreas Fault in the Tehachapi, San Emigdio, and Sierra Pelona Mountains.
The main shock of the 1857 Fort Tejon earthquake had an estimated duration of 5 to 10 minutes.
Answer: False
The main shock of the 1857 Fort Tejon earthquake lasted for an estimated duration of 1 to 3 minutes, not 5 to 10 minutes.
The San Andreas Fault is classified as a normal fault, characterized by vertical displacement of crustal blocks.
Answer: False
The San Andreas Fault is a strike-slip fault, meaning that the blocks of crust on either side move horizontally past each other, not vertically as in a normal fault.
The Pacific plate exhibits a northward movement relative to the Sierra Nevada-Great Valley Block of the North American plate at an approximate rate of 38 millimeters per year.
Answer: True
The source confirms that the Pacific plate moves north relative to the Sierra Nevada-Great Valley Block of the North American plate at approximately 38 millimeters per year.
The maximum offset observed along the San Andreas Fault during the 1857 earthquake measured 15 feet in the Carrizo Plain area.
Answer: False
The maximum offset recorded along the San Andreas Fault during the 1857 earthquake was 6 meters (20 feet) in the Carrizo Plain area, not 15 feet.
What was the estimated moment magnitude of the 1857 Fort Tejon earthquake?
Answer: 7.9
The source states that the 1857 Fort Tejon earthquake had an estimated moment magnitude of 7.9.
What is the rationale for referring to the 1857 earthquake as the 'Fort Tejon earthquake'?
Answer: It was the site where the greatest damage was observed.
The earthquake is named after Fort Tejon because it was the location where the greatest damage was observed, despite the actual epicenter being near Parkfield, California.
Which major geological fault experienced rupture during the 1857 Fort Tejon earthquake?
Answer: San Andreas Fault
The source explicitly states that the 1857 Fort Tejon earthquake ruptured the southern part of the San Andreas Fault.
What was the maximum perceived intensity of the 1857 Fort Tejon earthquake, as measured on the Modified Mercalli Intensity (MMI) scale?
Answer: IX (Violent)
The source indicates that the 1857 Fort Tejon earthquake had an estimated maximum perceived intensity of IX (Violent) on the Modified Mercalli Intensity scale.
What was the estimated duration of the main shock associated with the 1857 Fort Tejon earthquake?
Answer: 1 to 3 minutes
The source states that the main shock of the 1857 Fort Tejon earthquake lasted for an estimated duration of 1 to 3 minutes.
What geological classification describes the San Andreas Fault?
Answer: Strike-slip fault
The source identifies the San Andreas Fault as a strike-slip fault.
What is the approximate rate at which the Pacific plate moves northward relative to the Sierra Nevada-Great Valley Block?
Answer: 38 millimeters per year
The source states that the Pacific plate moves north relative to the Sierra Nevada-Great Valley Block of the North American plate at about 38 millimeters per year.
What was the maximum offset documented along the San Andreas Fault during the 1857 earthquake?
Answer: 6 meters (20 feet)
The source states that the maximum offset recorded along the San Andreas Fault during the 1857 earthquake was 6 meters (20 feet) in the Carrizo Plain area.
Paleoseismic studies have yielded no evidence of prehistoric earthquakes on the segment of the San Andreas Fault that ruptured in 1857.
Answer: False
Paleoseismic studies have, in fact, found evidence for many prehistoric earthquakes occurring in the last 3,000 years on this particular segment of the San Andreas Fault.
The slip of the 1857 earthquake likely ceased near Cajon Pass due to the prior release of tectonic stresses in that fault segment during the 1812 Wrightwood earthquake several decades prior.
Answer: True
The source indicates that the slip of the 1857 earthquake likely stopped near Cajon Pass because tectonic stresses in that area had been released by the 1812 Wrightwood earthquake.
The extreme southernmost portion of the San Andreas Fault, located near the Salton Sea, last experienced a rupture in the year 1857.
Answer: False
The extreme southernmost portion of the San Andreas Fault, near the Salton Sea, last ruptured in the year 1680, not 1857.
Researchers identified surface faulting extending north of Cholame into San Benito County through the analysis of satellite imagery.
Answer: False
Researchers identified surface faulting north of Cholame into San Benito County by recording first and second-hand accounts of ground cracks, not by analyzing satellite imagery.
Evidence of surface faulting observed south of Elizabeth Lake encompassed uprooted and displaced Jeffrey Pine trees, which formed a distinctive 'mole track'.
Answer: True
The source confirms that evidence of surface faulting south of Elizabeth Lake included uprooted and displaced Jeffrey Pine trees, forming a 'mole track'.
Tree ring dating indicated that Jeffrey Pines affected by the earthquake began to develop thinner rings on the side corresponding to the direction of the tilt.
Answer: False
Tree ring dating showed that Jeffrey Pines affected by the earthquake began to grow *twice as thick* rings on the side in the direction of the tilt, as a compensatory growth pattern, not thinner rings.
Foreshocks for the 1857 earthquake were reported to have occurred between one and nine hours prior to the main event, with their epicenter assumed to be near Fort Tejon.
Answer: False
While foreshocks occurred between one and nine hours before the main event, their epicenter is assumed to have been in the area between Parkfield and Cholame, approximately 97 kilometers (60 miles) northwest of Fort Tejon, not near Fort Tejon itself.
The absence of standardized timekeeping in 1857 California resulted in consistent and accurate reports regarding foreshock times.
Answer: False
The lack of standardized timekeeping in 1857 California, with local solar time in use, led to *inaccurate* reports of foreshock times, not consistent and accurate ones.
Sacramento and Los Angeles both reported experiencing the predawn, dawn, and sunrise foreshock events.
Answer: False
Sacramento and Los Angeles did not report experiencing any of the predawn, dawn, or sunrise foreshock events.
Seismologist Kerry Sieh hypothesized that the dawn and sunrise foreshocks were localized to coastal central California and likely possessed magnitudes between five and six.
Answer: True
The source confirms that seismologist Kerry Sieh theorized that the dawn and sunrise foreshocks were local to coastal central California and likely had magnitudes between five and six.
The regularity of Parkfield earthquakes assisted Kerry Sieh in determining the southeast boundary for the origination of the dawn foreshock.
Answer: True
The source states that the regularity of Parkfield earthquakes helped Kerry Sieh determine the southeast boundary for the origination of the dawn foreshock.
What insights did paleoseismic studies provide regarding the history of earthquakes on the 1857 rupture segment of the San Andreas Fault?
Answer: Evidence for many prehistoric earthquakes in the last 3,000 years.
Paleoseismic studies revealed evidence for many prehistoric earthquakes occurring in the last 3,000 years on this segment of the San Andreas Fault.
According to Thomas H. Jordan, what is the probable reason the 1857 earthquake rupture ceased near Cajon Pass?
Answer: The tectonic stresses had been released by the 1812 Wrightwood earthquake.
Thomas H. Jordan theorized that the 1857 earthquake rupture likely stopped near Cajon Pass because tectonic stresses in that area had been released by the 1812 Wrightwood earthquake.
In what year did the extreme southernmost portion of the San Andreas Fault, located near the Salton Sea, last experience a rupture?
Answer: 1680
The extreme southernmost portion of the San Andreas Fault, near the Salton Sea, last ruptured in the year 1680.
By what method did researchers identify surface faulting extending north of Cholame into San Benito County?
Answer: By recording first and second-hand accounts of ground cracks.
Researchers identified surface faulting extending north of Cholame into San Benito County by recording first and second-hand accounts of ground cracks.
What specific evidence of surface faulting was discovered south of Elizabeth Lake?
Answer: Uprooted and displaced Jeffrey Pine trees forming a 'mole track'.
Evidence of surface faulting found south of Elizabeth Lake included uprooted and displaced Jeffrey Pine trees forming a 'mole track'.
How did tree ring dating corroborate the effects of the 1857 earthquake on tilted Jeffrey Pines?
Answer: It revealed that tree rings grew twice as thick on the side in the direction of the tilt.
Tree ring dating confirmed that tree rings grew twice as thick on the side in the direction of the tilt, indicating a compensatory growth pattern due to the earthquake's effects.
What was a direct consequence of the absence of standardized timekeeping in California during 1857?
Answer: It led to inaccurate reports of when pre-shocks occurred.
The lack of standardized timekeeping in California during 1857 led to inaccurate reports of when pre-shocks occurred due to the use of local solar time.
Which two prominent California cities did not report experiencing any of the predawn, dawn, or sunrise foreshock events?
Answer: Sacramento and Los Angeles
Sacramento and Los Angeles did not report feeling any of the predawn, dawn, or sunrise foreshock events.
What was seismologist Kerry Sieh's theoretical assessment concerning the magnitude range of the dawn and sunrise foreshocks?
Answer: Between magnitude five and six
Seismologist Kerry Sieh theorized that the dawn and sunrise foreshocks most likely had magnitudes between five and six.
How did the observed regularity of Parkfield earthquakes contribute to the understanding of the 1857 foreshocks?
Answer: It helped determine the southeast boundary for the origination of the dawn foreshock.
The regularity of Parkfield earthquakes helped Kerry Sieh determine the southeast boundary for the origination of the dawn foreshock by comparing their felt reports.
At Fort Tejon, only minor cracks were observed in adobe buildings, and no injuries were documented.
Answer: False
At Fort Tejon, most of the adobe buildings were badly damaged, and several people sustained injuries, contradicting the statement that only minor cracks were observed and no injuries were reported.
The earthquake induced widespread hydrological effects, including disturbances to streams and springs in San Diego and Santa Barbara Counties, and rivers overflowing their banks.
Answer: True
The source confirms that the earthquake caused widespread hydrological effects, including disturbances in streams and springs in San Diego and Santa Barbara Counties, and rivers spilling over their banks.
The sparse population of California in 1857 facilitated easier and more accurate determination of intensity estimates due to a reduced number of structures requiring assessment.
Answer: False
The sparse population of California in 1857, while limiting overall damage, made intensity estimates *more challenging* due to fewer firsthand accounts, not easier.
Downtown Los Angeles experienced a maximum perceived intensity of VI, with some homes and buildings exhibiting cracks but no major structural damage.
Answer: True
The source confirms that downtown Los Angeles experienced a maximum perceived intensity of VI, with some homes and buildings showing cracks but no major damage.
Mission San Buenaventura's roof collapsed, and its bell tower sustained damage, concurrently with Mission Santa Cruz's front wall also collapsing.
Answer: True
The source confirms that Mission San Buenaventura's roof collapsed and its bell tower was damaged, and Mission Santa Cruz's front wall also collapsed.
The 1857 Fort Tejon earthquake led to a significant number of casualties, with over a dozen deaths reported.
Answer: False
Only two deaths were reported as a direct result of the 1857 Fort Tejon earthquake, not over a dozen.
What type of damage was sustained by the adobe buildings located at Fort Tejon?
Answer: Most were badly damaged
At Fort Tejon, most of the adobe buildings were badly damaged, not just showing minor cracks or no damage.
Which of the following was NOT identified as a widespread hydrological effect observed subsequent to the earthquake?
Answer: Significant tsunamis along the California coast.
The source lists disturbances in streams and springs, rivers spilling over banks, and affected well water flow as hydrological effects, but does not mention significant tsunamis.
In which locations were ground cracks, indicative of soil liquefaction, observed following the earthquake?
Answer: In swampy ground near the Pueblo de Los Angeles and in the Oxnard Plain.
Ground cracks resulting from soil liquefaction were observed in swampy ground near the Pueblo de Los Angeles and in the Oxnard Plain.
How did California's sparse population in 1857 influence the reported damage and the accuracy of intensity estimates for the earthquake?
Answer: It limited overall damage but made intensity estimates more challenging due to fewer accounts.
The sparse population of California in 1857 limited overall damage but made intensity estimates more challenging due to a reduced number of firsthand accounts.
What was the maximum perceived intensity recorded in downtown Los Angeles during the 1857 earthquake?
Answer: MMI VI
Downtown Los Angeles experienced a maximum perceived intensity of VI on the Modified Mercalli scale during the 1857 earthquake.
What specific damage was documented at Mission San Buenaventura?
Answer: The roof collapsed, and its bell tower was damaged.
At Mission San Buenaventura, the roof collapsed, and its bell tower was damaged.
How many fatalities were reported as a direct consequence of the 1857 Fort Tejon earthquake?
Answer: Two
Two deaths were reported as a direct result of the 1857 Fort Tejon earthquake.
The largest aftershock on January 16, 1857, possessed an estimated magnitude of about 6.7 and generated high felt intensities in Santa Barbara, San Bernardino, and Los Angeles.
Answer: True
The source confirms that the largest aftershock on January 16, 1857, had an estimated magnitude of about 6.7 and resulted in high felt intensities in Santa Barbara, San Bernardino, and Los Angeles.
Scientists speculate that future slip along the San Andreas Fault segment that ruptured in 1857 might be characterized by frequent, smaller seismic events.
Answer: False
Scientists suggest that future slip along the San Andreas Fault segment that ruptured in 1857 may be characterized by *another very large 1857-type event*, followed by another period of inactivity, not frequent, smaller events.
The Los Angeles Aqueduct and the California Aqueduct are vulnerable to a recurrence of the 1857 earthquake, as they traverse the San Andreas Fault within the primary damage zone.
Answer: True
The source confirms that the Los Angeles Aqueduct and the California Aqueduct are vulnerable to a repeat of the 1857 earthquake because they cross the San Andreas Fault within the main damage zone.
What was the estimated magnitude of the largest aftershock that occurred on January 16, 1857?
Answer: About 6.7
The largest aftershock on January 16, 1857, had an estimated magnitude of about 6.7.
Which of the following communities are located in close proximity to the San Andreas Fault within the potential future rupture zone, analogous to the 1857 event?
Answer: Frazier Park, Palmdale, and Wrightwood
The communities of Frazier Park, Palmdale, and Wrightwood are situated very close to the San Andreas Fault within the potential future rupture zone similar to 1857.
According to Swaminathan Krishnan, which specific area would be particularly severely affected if a similar rupture from Parkfield to Wrightwood were to recur?
Answer: The San Fernando Valley
According to Swaminathan Krishnan, the San Fernando Valley would be particularly hard hit if a similar rupture from Parkfield to Wrightwood were to happen again.