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1987 Whittier Narrows Earthquake
The 1987 Whittier Narrows earthquake occurred in the southern San Gabriel Valley and surrounding communities of Southern California, United States, at on October 1. The moderate magnitude 5.9 blind thrust earthquake was centered several miles north of Whittier in the town of Rosemead, had a relatively shallow depth, and was felt throughout southern California and southern Nevada. Many homes and businesses were affected, along with roadway disruptions, mainly in Los Angeles and Orange counties. 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 (''Strong'') to VII (''Very strong''). Only Whittier experienced a level of VIII (''Severe''), the highest experienced during the event, with the historic uptown area suffering the greatest damage. A separate M5.2 strike-slip event occurred ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pacific Daylight Time
The Pacific Time Zone (PT) is a time zone encompassing parts of western Canada, the western United States, and western Mexico. Places in this zone observe standard time by subtracting eight hours from Coordinated Universal Time ( UTC−08:00). During daylight saving time, a time offset of UTC−07:00 is used. In the United States and Canada, this time zone is generically called the Pacific Time Zone. Specifically, time in this zone is referred to as Pacific Standard Time (PST) when standard time is being observed (early November to mid-March), and Pacific Daylight Time (PDT) when daylight saving time (mid-March to early November) is being observed. In Mexico, the corresponding time zone is known as the ''Zona Noroeste'' (Northwest Zone) and observes the same daylight saving schedule as the U.S. and Canada. The largest city in the Pacific Time Zone is Los Angeles, whose metropolitan area is also the largest in the time zone. The zone is two hours ahead of the Hawaii–Aleut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mercalli Intensity Scale
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the effects of an earthquake at a given location, distinguished from the earthquake's inherent force or strength as measured by seismic magnitude scales (such as the "" magnitude usually reported for an earthquake). While shaking is caused by the seismic energy released by an earthquake, earthquakes differ in how much of their energy is radiated as seismic waves. Deeper earthquakes also have less interaction with the surface, and their energy is spread out across a larger volume. Shaking intensity is localized, generally diminishing with distance from the earthquake's epicenter, but can be amplified in sedimentary basins and certain kinds of unconsolidated soils. Intensity scales empirically categorize the intensity of shaking based on the effect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P Wave
A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any affected location or at a seismograph. P waves may be transmitted through gases, liquids, or solids. Nomenclature The name ''P wave'' can stand for either pressure wave (as it is formed from alternating compressions and rarefactions) or primary wave (as it has high velocity and is therefore the first wave to be recorded by a seismograph). The name ''S wave'' represents another seismic wave propagation mode, standing for secondary or shear wave. Seismic waves in the Earth Primary and secondary waves are body waves that travel within the Earth. The motion and behavior of both P and S waves in the Earth are monitored to probe the interior structure of the Earth. Discontinuities in velocity as a function of depth are indicative of change ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Whittier Narrows
The Whittier Narrows is a narrows or water gap in the San Gabriel Valley of Los Angeles County, California, United States, between the Puente Hills to the east and the Montebello Hills to the west. The gap is located at the southern boundary of the San Gabriel Valley, through which the Rio Hondo and the San Gabriel River flow to enter the Los Angeles Basin. The Narrows is located near the convergence of Interstate 605 (the San Gabriel River Freeway) and California State Route 60 (the Pomona Freeway). History The first European land exploration of Alta California, the Spanish Portolá expedition, discovered Whittier Narrows on its return journey to San Diego. On the outbound journey, the party had followed San Jose Creek, reaching the San Gabriel River north of the Narrows. Franciscan missionary Juan Crespi noted in his diary, "We started out in the morning through the gap of the valley of San Miguel ow San Gabriel which is very full of trees. We traveled a long while to the sout ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambridge University Press
Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by Henry VIII of England, King Henry VIII in 1534, it is the oldest university press A university press is an academic publishing house specializing in monographs and scholarly journals. Most are nonprofit organizations and an integral component of a large research university. They publish work that has been reviewed by schola ... in the world. It is also the King's Printer. Cambridge University Press is a department of the University of Cambridge and is both an academic and educational publisher. It became part of Cambridge University Press & Assessment, following a merger with Cambridge Assessment in 2021. With a global sales presence, publishing hubs, and offices in more than 40 Country, countries, it publishes over 50,000 titles by authors from over 100 countries. Its publishing includes more than 380 academic journals, monographs, reference works, school and uni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strike And Dip
Strike and dip is a measurement convention used to describe the orientation, or attitude, of a planar geologic feature. A feature's strike is the azimuth of an imagined horizontal line across the plane, and its dip is the angle of inclination measured downward from horizontal. They are used together to measure and document a structure's characteristics for study or for use on a geologic map. A feature's orientation can also be represented by dip and dip direction, using the azimuth of the dip rather than the strike value. Linear features are similarly measured with trend and plunge, where "trend" is analogous to dip direction and "plunge" is the dip angle. Strike and dip are measured using a compass and a clinometer. A compass is used to measure the feature's strike by holding the compass horizontally against the feature. A clinometer measures the features dip by recording the inclination perpendicular to the strike. These can be done separately, or together using a tool such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Puente Hills
The Puente Hills are a chain of hills, one of the lower Transverse Ranges, in an unincorporated area in eastern Los Angeles County, California, in the United States. The western end of the range is often referred to locally as the Whittier Hills. Geography The Puente Hills lie to the south of the San Gabriel Valley and the Pomona Freeway ( State Route 60), to the east of the San Gabriel River Freeway (Interstate 605), to the north of Whittier Boulevard, and to the west of the city of Diamond Bar and Chino Hills. To its north are the City of Industry, Hacienda Heights, and Rowland Heights. To the south are Whittier, La Habra Heights, La Habra and Brea. The Brea-Olinda Oil Field, discovered in 1880 and still producing in 2014, is in the southernmost portion of the hills adjacent to the city of Brea. Flora The Puente Hills are in the California chaparral and woodlands ecoregion of the California Floristic Province. The remnant California native plants here are in the chaparral ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflection Seismology
Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite or Tovex blast, a specialized air gun or a seismic vibrator. Reflection seismology is similar to sonar and echolocation. This article is about surface seismic surveys; for vertical seismic profiles, see VSP. History Reflections and refractions of seismic waves at geologic interfaces within the Earth were first observed on recordings of earthquake-generated seismic waves. The basic model of the Earth's deep interior is based on observations of earthquake-generated seismic waves transmitted through the Earth's interior (e.g., Mohorovičić, 1910). The use of human-generated seismic waves to map in detail the geology of the upper few kilometers of the Earth's crust followed shortly thereafter and h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focal Mechanism
The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a fault-plane solution. Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an analysis of observed seismic waveforms. The focal mechanism can be derived from observing the pattern of "first motions", that is, whether the first arriving P waves break up or down. This method was used before waveforms were recorded and analysed digitally and this method is still used for earthquakes too small for easy moment tensor solution. Focal mechanisms are now mainly derived using semi-automatic analysis of the recorded waveforms. Moment tensor solutions The moment tensor solution is typically displayed graphically using a so-called ''beachball'' diagram. The pattern of en ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Puente Hills Fault
The Puente Hills Fault (also known as the Puente Hills Thrust Fault System) is an active geological fault that is located in the Los Angeles Basin in California. The thrust fault was discovered in 1999 and runs about in three discrete sections from the Puente Hills region in the southeast to just south of Griffith Park in the northwest. The fault is known as a blind thrust fault, as the fault plane does not extend to the surface. Large earthquakes on the fault are relatively infrequent but computer modeling has indicated that a major event could have substantial impact in the Los Angeles area. The fault is now thought to be responsible for one moderate earthquake in 1987 (the 1987 Whittier Narrows earthquake) and another light event that took place in 2010, with the former causing considerable damage and deaths. Geology The Los Angeles Basin is situated along the coast of Southern California at the confluence of the Transverse Ranges and the Peninsular Ranges. The basin is unde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
California Coast Ranges
The Coast Ranges of California span from Del Norte or Humboldt County, California, south to Santa Barbara County. The other three coastal California mountain ranges are the Transverse Ranges, Peninsular Ranges and the Klamath Mountains. Physiographically, they are a section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System physiographic division. UNESCO has included the "California Coast Ranges Biosphere Reserve" in its Man and the Biosphere Programme of World Network of Biosphere Reserves since 1983. * Physiography The northern end of the California Coast Ranges overlap the southern end of the Klamath Mountains for approximately 80 miles on the west. They extend southward for more than 600 miles to where the coastline turns eastward along the Santa Barbara Channel, around the area of Point Conception. Here the southern end meets the Los Angeles Transverse Ranges, or ''Sierras de los Angeles''. The rocks themselves that com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1983 Coalinga Earthquake
The 1983 Coalinga earthquake struck at 4:42 p.m. Monday, May 2 of that year, in Coalinga, California. The shock was felt from the Greater Los Angeles Area north to Susanville in Lassen County, and between the Pacific Coast and western Nevada. More than 5,000 aftershocks were recorded through July 31, of which 894 had a magnitude of 2.5 or larger. It measured 6.2 on the moment magnitude scale and had a maximum Mercalli intensity of VIII (''Severe''). Earthquake The Coalinga quake was caused by an 0.5-meter uplift of an anticline ridge northeast of Coalinga, but surface faulting was not observed. Ground and aerial reconnaissance immediately after the quake revealed ground cracks and fissures within about of the epicenter, none of which appeared to represent movement on deeply rooted fault structures. About five weeks later, on June 11, an aftershock caused surface faulting about northwest of Coalinga. Damage The earthquake caused an estimated $10 million in property dama ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
