Piercing point

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Microfault showing an example of a piercing point. The base of the white bed (layer), shown with red arrows, is an indication of the amount of offset on this fault. The fault is coated orange and runs from the upper left to the lower right of the picture, truncating the white bed. U.S. dime for scale. Microfault.jpg
Microfault showing an example of a piercing point. The base of the white bed (layer), shown with red arrows, is an indication of the amount of offset on this fault. The fault is coated orange and runs from the upper left to the lower right of the picture, truncating the white bed. U.S. dime for scale.

In geology, a piercing point is defined as a feature (usually a geologic feature, preferably a linear feature) that is cut by a fault, then moved apart. [1] Reconfiguring the piercing point back in its original position is the primary way geologists can find out the minimum slip, or displacement, along a fault. This can be done on a large scale (over many kilometers [2] ), a small scale (inside a single outcrop or fault trench [3] ) or even a single hand sample/rock (see image).

Items that are usually used in a piercing point study include large geologic formations or other rock units that can be matched either stratigraphically, geochemically, or by age dating. Features that are linear or planar, like a stratigraphic unit, are much better for use in a piercing point study than rounds or irregular-shaped objects, such as a pluton, because the reconstruction is always more precise with a more predictable shape (because of the Principle of lateral continuity). Of course, it is important to keep in mind that piercing points only give a minimum amount of offset that fault could have taken. In certain situations, rock units can be created as fault movement occurs, making the piercing point measurement even less than a minimum value.[ citation needed ]

Mason Hill and Thomas Dibblee were the first to use piercing points along the San Andreas fault, notably the Pelona schist in the San Gabriel Mountains and Orocopia schist in the Orocopia Mountains, in 1953; [4] they showed at least 250 km (160 mi) of slip using that piercing point. [5] [6] Another famous example of San Andreas fault piercing points include the unique rocks at Point Lobos State Reserve and Point Reyes National Seashore. [7] [8] Though 180 km apart, the rocks match exactly: they were cut and separated by the fault. A complete, detailed analysis shows that the movement, while uncertain because of the various piercing points used, is over 300 km (190 mi) since the Miocene. [6] [9] Piercing points are used on faults other than the San Andreas, like the Hilina fault system in Hawaii [10] and the Lake Clark fault system in Alaska. [11]

In rare situations, even human structures built across a fault can be used, like an Ottoman Empire-era canal berm that was offset along the North Anatolian fault zone in a 1754 earthquake and the 1999 Izmit earthquake in Turkey. [12] The berm showed 3–4 meters (9.8–13.1 ft) of movement in the 1999 earthquake. [12]

Related Research Articles

<span class="mw-page-title-main">San Andreas Fault</span> Geologic feature in California

The San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the U.S. state of California. It forms part of the tectonic boundary between the Pacific Plate and the North American Plate. Traditionally, for scientific purposes, the fault has been classified into three main segments, each with different characteristics and a different degree of earthquake risk. The average slip rate along the entire fault ranges from 20 to 35 mm per year.

<span class="mw-page-title-main">Thrust fault</span> Type of reverse fault that has a dip of 45 degrees or less

A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.

<span class="mw-page-title-main">Transform fault</span> Plate boundary where the motion is predominantly horizontal

A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone. A transform fault is a special case of a strike-slip fault that also forms a plate boundary.

<span class="mw-page-title-main">Fault (geology)</span> Fracture or discontinuity in displaced rock

In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Faults may also displace slowly, by aseismic creep.

<span class="mw-page-title-main">Transverse Ranges</span> Group of mountain ranges of southern California

The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges physiographic region in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie within Santa Barbara, Ventura, Los Angeles, San Bernardino, Riverside and Kern counties. The Peninsular Ranges lie to the south. The name Transverse Ranges is due to their east–west orientation, making them transverse to the general northwest–southeast orientation of most of California's coastal mountains.

<span class="mw-page-title-main">Los Angeles Basin</span> Sedimentary basin located along the coast of southern California

The Los Angeles Basin is a sedimentary basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an anomalous group of east-west trending chains of mountains collectively known as the Transverse Ranges. The present basin is a coastal lowland area, whose floor is marked by elongate low ridges and groups of hills that is located on the edge of the Pacific Plate. The Los Angeles Basin, along with the Santa Barbara Channel, the Ventura Basin, the San Fernando Valley, and the San Gabriel Basin, lies within the greater Southern California region. The majority of the jurisdictional land area of the city of Los Angeles physically lies within this basin.

<span class="mw-page-title-main">Vasquez Rocks</span> Natural area park in Agua Dulce, California

Vasquez Rocks Natural Area Park is a 932-acre (377-hectare) park located in the Sierra Pelona in northern Los Angeles County, California. It is known for its rock formations, the result of sedimentary layering and later seismic uplift. It is located near the town of Agua Dulce, between the cities of Santa Clarita and Palmdale. The area is visible from the Antelope Valley Freeway. Its location approximately 25 miles (40 km) from downtown Los Angeles places it within Hollywood's "studio zone" and makes it a popular filming location for films and television programs.

<span class="mw-page-title-main">Orocopia Mountains</span> Mountain range of the Transverse Ranges in California, United States

The Orocopia Mountains are located in Riverside County in southern California, United States, east of the Coachella Valley, west of the Chuckwalla Mountains, and south of Interstate 10 in the Colorado Desert. The range lies in an east-west direction, and is approximately 18 miles long. The Orocopia Mountains are north of and overlooking the Salton Sea and south of Joshua Tree National Park, with the Chocolate Mountains to the southeast and the scenic Mecca Hills just northwest.

<span class="mw-page-title-main">Newport–Inglewood Fault</span> Fault in Southern California

The Newport–Inglewood Fault is a right-lateral strike-slip fault in Southern California. The fault extends for 47 mi (76 km) from Culver City southeast through Inglewood and other coastal communities to Newport Beach at which point the fault extends east-southeast into the Pacific Ocean where it is known as the Rose Canyon Fault. The fault can be inferred on the Earth's surface as passing along and through a line of hills extending from Signal Hill to Culver City. The fault has a slip rate of approximately 0.6 mm (0.024 in)/year and is predicted to be capable of a 6.0–7.4 magnitude earthquake on the moment magnitude scale. A 2017 study concluded that, together, the Newport–Inglewood Fault and Rose Canyon Fault could produce an earthquake of 7.3 or 7.4 magnitude.

<span class="mw-page-title-main">Thrust tectonics</span> Concept in structural geology

Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, the others being extensional tectonics and strike-slip tectonics. These match the three types of plate boundary, convergent (thrust), divergent (extensional) and transform (strike-slip). There are two main types of thrust tectonics, thin-skinned and thick-skinned, depending on whether or not basement rocks are involved in the deformation. The principle geological environments where thrust tectonics is observed are zones of continental collision, restraining bends on strike-slip faults and as part of detached fault systems on some passive margins.

Strike-slip tectonics or wrench tectonics is a type of tectonics that is dominated by lateral (horizontal) movements within the Earth's crust. Where a zone of strike-slip tectonics forms the boundary between two tectonic plates, this is known as a transform or conservative plate boundary. Areas of strike-slip tectonics are characterised by particular deformation styles including: stepovers, Riedel shears, flower structures and strike-slip duplexes. Where the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either transpressional or transtensional depending on the sense of deviation. Strike-slip tectonics is characteristic of several geological environments, including oceanic and continental transform faults, zones of oblique collision and the deforming foreland of zones of continental collision.

The Walker Lane is a geologic trough roughly aligned with the California/Nevada border southward to where Death Valley intersects the Garlock Fault, a major left lateral, or sinistral, strike-slip fault. The north-northwest end of the Walker Lane is between Pyramid Lake in Nevada and California's Lassen Peak where the Honey Lake Fault Zone, the Warm Springs Valley Fault, and the Pyramid Lake Fault Zone meet the transverse tectonic zone forming the southern boundary of the Modoc Plateau and Columbia Plateau provinces. The Walker Lane takes up 15 to 25 percent of the boundary motion between the Pacific Plate and the North American Plate, the other 75 percent being taken up by the San Andreas Fault system to the west. The Walker Lane may represent an incipient major transform fault zone which could replace the San Andreas as the plate boundary in the future.

In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping strike-slip faults or a fault bend create an area of crustal extension undergoing tension, which causes the basin to sink down. Frequently, the basins are rhombic or sigmoidal in shape. Dimensionally, basins are limited to the distance between the faults and the length of overlap.

<span class="mw-page-title-main">Coyote Mountains</span> Mountain range in California, United States

The Coyote Mountains are a small mountain range in San Diego and Imperial Counties in southern California. The Coyotes form a narrow ESE trending 2 mi (3.2 km) wide range with a length of about 12 mi (19 km). The southeast end turns and forms a 2 mi (3.2 km) north trending "hook". The highest point is Carrizo Mountain on the northeast end with an elevation of 2,408 feet (734 m). Mine Peak at the northwest end of the range has an elevation of 1,850 ft (560 m). Coyote Wash along I-8 along the southeast margin of the range is 100 to 300 feet in elevation. Plaster City lies in the Yuha Desert about 5.5 mi (8.9 km) east of the east end of the range.

<span class="mw-page-title-main">Jalama Formation</span> Sedimentary rock formation in California, United States

The Jalama Formation is a sedimentary rock formation widespread in southern Santa Barbara County and northern Ventura County, southern California. Of the Late Cretaceous epoch, the unit consists predominantly of clay shale with some beds of sandstone.

The 1991 Sierra Madre earthquake occurred on June 28 at 07:43:55 local time with a moment magnitude of 5.6 and a maximum Mercalli intensity of VII. The thrust earthquake resulted in two deaths, around 100 injuries, and damage estimated at $33.5–40 million. The event occurred beneath the San Gabriel Mountains on the Clamshell–Sawpit Fault, which is a part of the Sierra Madre–Cucamonga Fault System. Instruments captured the event at a number of strong motion stations in Southern California.

<span class="mw-page-title-main">Geology of Myanmar</span>

The geology of Myanmar is shaped by dramatic, ongoing tectonic processes controlled by shifting tectonic components as the Indian plate slides northwards and towards Southeast Asia. Myanmar spans across parts of three tectonic plates separated by north-trending faults. To the west, a highly oblique subduction zone separates the offshore Indian plate from the Burma microplate, which underlies most of the country. In the center-east of Myanmar, a right lateral strike slip fault extends from south to north across more than 1,000 km (620 mi). These tectonic zones are responsible for large earthquakes in the region. The India-Eurasia plate collision which initiated in the Eocene provides the last geological pieces of Myanmar, and thus Myanmar preserves a more extensive Cenozoic geological record as compared to records of the Mesozoic and Paleozoic eras. Myanmar is physiographically divided into three regions: the Indo-Burman Range, Myanmar Central Belt and the Shan Plateau; these all display an arcuate shape bulging westwards. The varying regional tectonic settings of Myanmar not only give rise to disparate regional features, but they also foster the formation of petroleum basins and a diverse mix of mineral resources.

<span class="mw-page-title-main">Geology and geological history of California</span> Description of the geology of California

The geology of California is highly complex, with numerous mountain ranges, substantial faulting and tectonic activity, rich natural resources and a history of both ancient and comparatively recent intense geological activity. The area formed as a series of small island arcs, deep-ocean sediments and mafic oceanic crust accreted to the western edge of North America, producing a series of deep basins and high mountain ranges.

The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST in the geologically active Salton Trough of Southern California. The Salton Trough represents a pull-apart basin formed by movements along major faults. This region is dominated by major strike-slip faults one of them being the San Jacinto Fault which produced the 1968 earthquake. The mainshock's epicenter was near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). The zone of surface rupture was assigned a maximum Modified Mercalli intensity (MMI) of VII.

<span class="mw-page-title-main">Vasquez Formation</span> Late Oligocene to Early Miocene sedimentary formation in the Sierra Pelona of California

The Vasquez Formation (Tvz) is a geologic formation cropping out at the eponymous Vasquez Rocks in southern California. The formation dates to the Late Oligocene to Early Miocene.

References

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  2. Richard Oliver Lease, Nadine McQuarrie, Michael Oskin, and Andrew Leier, 2009, Quantifying Dextral Shear on the Bristol-Granite Mountains Fault Zone: Successful Geologic Prediction from Kinematic Compatibility of the Eastern California Shear Zone, Journal of Geology, Volume 117, p. 37–53
  3. S Baker, 2005, Pseudotachylyte-generating faults in Central Otago, New Zealand, Tectonophysics, Volume: 397, Issue: 3-4, Publisher: Elsevier, Pages: 211-223
  4. Hill, M.L., and Dibblee, T.W., Jr., 1953, San Andreas, Garlock, and Big Pine faults, California-a study of the character, history, and tectonic significance of their displacements: Geological Society of America Bulletin, v. 64, no. 4, p. 443-458.
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  6. 1 2 Naeim, Farzad (1992–1994). "DISPLACEMENT OF BASEMENT ROCKS BY THE SAN ANDREAS FAULT". An overview of the history, geology, geomorphology, geophysics, and seismology of the most well-known plate-tectonics boundary in the world. John A. Martin and Associates, Inc. Retrieved June 24, 2012.
  7. Kathleen Burnham, Update Re: Predictive Late Cretaceous to Early Miocene Paleogeography of the San Andreas Fault System Derived from Detailed Multidisciplinary Conglomerate Correlations, AAPG Search and Discovery Article #90076©2008 AAPG Pacific Section, Bakersfield, California
  8. Alden, Andrew (June 6, 2008). "A World-Class Piercing Point". About.com. Archived from the original on March 15, 2012. Retrieved June 24, 2012.
  9. Huffman, O.F., 1972, Lateral displacement of Upper Miocene rocks and the Neogene history of offset along the San Andreas fault in central California: Geological Society of America Bulletin, v. 83, no. 10, p. 2913-2946.
  10. Complete Report for Hilina fault system, 'Apua Pali section (Class A) No. 2610m
  11. 26 km of Offset on the Lake Clark Fault Since Late Eocene Time
  12. 1 2 "SCEC Geologic Investigations of the August 17, 1999 Izmit, Turkey Earthquake". Archived from the original on January 8, 2013. Retrieved June 19, 2012.