World Library  
Flag as Inappropriate
Email this Article

Blind thrust earthquake

Article Id: WHEBN0000235619
Reproduction Date:

Title: Blind thrust earthquake  
Author: World Heritage Encyclopedia
Language: English
Subject: 1987 Whittier Narrows earthquake, 1983 Coalinga earthquake, Aftershock, Body wave magnitude, Adams–Williamson equation
Collection: Types of Earthquake
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Blind thrust earthquake

A blind thrust earthquake occurs along a thrust fault that does not show signs on the Earth's surface, hence the designation "blind".[1] 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; 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.

Contents

  • Blind thrust faults 1
  • Examples of occurrence 2
    • Some known faults 2.1
    • Specific events 2.2
  • References 3

Blind thrust faults

Blind thrust faults generally exist near tectonic plate 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 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 profiles[2] show the disturbed rock that hides a blind thrust fault.

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.

It is said that blind thrust earthquakes contribute more to urban seismic risk than the 'big ones' of magnitude 8 or more.[3]

Examples of occurrence

Some known faults

  • 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.[4][5] A NASA study which combined satellite radar images and Global Positioning System (GPS) observations [6] found that "the tectonic squeezing across Los Angeles will likely produce earthquakes on either the blind Elysian Park or Puente Hills thrust fault systems".
  • Bajo Segura Fault Zone, Spain
  • Fukaya Fault System, Japan (near Tokyo)
  • Uemachi Fault System, Osaka Basin, Japan

Specific events

References

  1. ^ http://earthquake.usgs.gov/learning/glossary.php?term=blind%20thrust%20fault
  2. ^ http://web.archive.org/web/20050305030422/http://faculty.washington.edu/tpratt/GRL02.pdf
  3. ^ , "7.5 quake on California fault could be disastrous", 30 March 2014Washington Post: accessed 30 March 2014.
  4. ^ http://www.agu.org/pubs/crossref/1996/95JB03453.shtml
  5. ^ http://www.sciencemag.org/cgi/content/abstract/283/5407/1516?ck=nck
  6. ^ http://quake.usgs.gov/research/deformation/modeling/socal/index_gerald.html
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.