A blind thrust earthquake occurs along a

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. I ...

that does not show signs on the Earth's surface, hence the designation "blind". Such faults, being invisible at the surface, have not been mapped by standard surface geological mapping. Sometimes they are discovered as a by-product of oil exploration

seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

; in other cases their existence is not suspected. Although such earthquakes are not amongst the most energetic, they are sometimes the most destructive, as conditions combine to form an urban earthquake which greatly affects urban seismic risk. A blind thrust earthquake is quite close, in meaning, to a buried rupture earthquake, if a buried rupture earthquake is not specifically about the fault, but signs the earthquake leaves, on the Earth's surface.

Blind thrust faults

Blind thrust faults generally exist near

tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

margins, in the broad disturbance zone. They form when a section of the Earth's crust is under high compressive stresses, due to plate margin collision, or the general geometry of how the plates are sliding past each other. As shown in the diagram, a weak plate under compression generally forms thrusting sheets, or overlapping sliding sections. This can form a hill and valley landform, with the hills being the strong sections, and the valleys being the highly disturbed thrust faulted and folded sections. After a long period of

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

the visible landscape may be flattened, with material eroded from the hills filling up the valleys and hiding the underlying hill-and-valley geology. The valley rock is very weak and usually highly weathered, presenting deep, fertile soil; naturally, this is the area that becomes populated.

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 reflection (physics), reflected seismic waves. The method requir ...

profiles show the disturbed rock that hides a blind

. If the region is under active compression these faults are constantly rupturing, but any given valley might only experience a large earthquake every few hundred years. Although usually of magnitude 6 to 7 compared to the largest magnitude 9 earthquakes of recent times, such a temblor is especially destructive because the seismic waves are highly directed, and the soft basin soil of the valley can amplify the ground motions tenfold or more.

Examples of occurrence

Some known faults

Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

, California, USA, has many earthquakes and is well-studied. In addition to surface faults, a number of blind-thrust faults have been found under the basin and metropolitan area. A

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

study which combined satellite radar images and

Global Positioning System The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...

(GPS) observations found that "tectonic squeezing across Los Angeles" "will likely produce earthquakes on either the blind Elysian Park or

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, Los Angeles County, California, in the United States. The western end of the range is often referred to ...

thrust fault systems". A blind thrust earthquake along the Puente Hills fault could contribute more to urban seismic risk than the 'big ones' of magnitude 8 or more.''Washington Post'', "7.5 quake on California fault could be disastrous", 30 March 2014
accessed 30 March 2014. * Bajo Segura Fault Zone, Spain * Fukaya Fault System, Japan (near Tokyo) * Uemachi Fault System, Osaka Basin, Japan * Main Frontal Thrust, Himalaya

Blind thrust faults

Examples of occurrence

Some known faults

Specific events

See also

References

External links