geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

, 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. Reconfiguring the piercing point back in its original position is the primary way

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althoug ...

s can find out the minimum slip, or displacement, along a fault. This can be done on a large scale (over many kilometers), a small scale (inside a single outcrop or fault trench) 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 a 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 The principle of lateral continuity states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or oth ...

). 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. Mason Hill and

Thomas Dibblee Thomas Wilson Dibblee, Jr. (11 October 1911, in Santa Barbara, California – 17 November 2004, in Santa Barbara, California) was an American geologist best known for his geological mapping. He is also known, together with co-author Mason H ...

were the first to use piercing points along the

San Andreas fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizonta ...

, notably the Pelona schist in the San Gabriel Mountains and Orocopia schist in the

Orocopia Mountains 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 dire ...

, in 1953; they showed at least of slip using that piercing point. Another famous example of San Andreas fault piercing points include the unique rocks at

Point Lobos State Reserve Point or points may refer to: Places * Point, Lewis, a peninsula in the Outer Hebrides, Scotland * Point, Texas, a city in Rains County, Texas, United States * Point, the NE tip and a ferry terminal of Lismore, Inner Hebrides, Scotland * Poin ...

and

Point Reyes National Seashore Point Reyes National Seashore is a park preserve located on the Point Reyes Peninsula in Marin County, California. As a national seashore, it is maintained by the US National Park Service as an important nature preserve. Some existing agricult ...

. 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 since the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

. Piercing points are used on faults other than the San Andreas, like the Hilina fault system in

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...

and the Lake Clark fault system in

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S. ...

.26 km of Offset on the Lake Clark Fault Since Late Eocene Time
/ref> In rare situations, even human structures built across a fault can be used, like an

Ottoman Empire The Ottoman Empire, * ; is an archaic version. The definite article forms and were synonymous * and el, Оθωμανική Αυτοκρατορία, Othōmanikē Avtokratoria, label=none * info page on book at Martin Luther University) ...

-era canal berm that was offset along the

North Anatolian fault The North Anatolian Fault (NAF) ( tr, Kuzey Anadolu Fay Hattı) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian Plate and the Anatolian Plate. The fault extends westward fro ...

zone in a 1754 earthquake and the 1999 Izmit earthquake in

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula in ...

. The berm showed of movement in the 1999 earthquake.

References

{{Reflist Structural geology Seismic faults Measurement