A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.
OF the most simple to understand types of faults are:
normal fault - a dip-slip fault in which the block above the fault has moved downward relative to the block below. This type of faulting occurs in response to extension and is often observed in the Western United States Basin and Range Province and along oceanic ridge systems.
Normal Fault Animation
thrust fault - a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block. This type of faulting is common in areas of compression, such as regions where one plate is being subducted under another as in Japan. When the dip angle is shallow, a reverse fault is often described as a thrust fault.
Thrust Fault Animation
strike-slip fault - a fault on which the two blocks slide past one another. The San Andreas Fault is an example of a right lateral fault.
Strike-slip Fault Animation
(Source: USGS)
Based on the information provided and the schematic above, at the coordinates of this EC you have a well defined normal fault. In order to validate your FIND, you need to answer the following questions:
- Facing the outcrop, which side has moved down? (LEFT, i.e., North or RIGHT, i.e., South?)
- What is the amount of movement (in metres or centimetres)?
- What is the angle of the fault plane in relation to the vertical?
If you have the answers, send them along to me with the ID of the cache.
Thank you for visiting.
O que é uma falha?
Uma falha geológica resulta da ruptura ou cisão de um bloco de rochas ou faixas estreitas da superfície que é responsável pelo deslocamento das suas partes. Este fenómeno geológico surge em função da pressão aplicada por uma força, em que a pressão exercida excede a capacidade de resistência e plasticidade das camadas rochosas, provocando a sua cisão ou ruptura, podendo gerar também algumas pequenas fraturas em seu entorno.
Tipos de falhas:
Em função da sua inclinação, as falhas são classificadas como:
- Falhas normais;
- Falhas inversas;
- Falhas de desligamento.
Esta EarthCache lida apenas com as falhas normais. Neste caso o plano de falha é normalmente muito inclinado e um dos lados desloca-se para baixo. Ver animação infra:
Strike-slip Fault Animation
(Fonte: USGS)
Para poderes fazer o registo desta EC, precisas de responder às seguintes perguntas e enviá-las para mim com o ID da cache:
- Posiciona-te de frente para o afloramento. Qula o lado que desceu em relaçáo ao outro? (ESQUERDO - NORTE ou DIREITO - SUL)
- Mede a distância de movimento (em metros ou centímetros)?
- Qual o ângulo que o plano de falha faz com a vertical?
Obrigado pela visita.
The most exciting way to learn about the Earth and its processes is to get into the outdoors and experience it first-hand. Visiting an Earthcache is a great outdoor activity the whole family can enjoy.
An Earthcache is a special place that people can visit to learn about a unique geoscience feature or aspect of our Earth. Earthcaches include a set of educational notes and the details about where to find the location (latitude and longitude). Visitors to Earthcaches can see how our planet has been shaped by geological processes, how we manage the resources and how scientists gather evidence to learn about the Earth. To find out more click HERE.