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In physical geography and geology, a horst is a raised fault block bounded by normal faults. [1] Horsts are typically found together with grabens. While a horst is lifted or remains stationary, the grabens on either side subside. [2] This is often caused by extensional forces pulling apart the crust.
The Philippine fault system is a major inter-related system of geological faults throughout the whole of the Philippine Archipelago, [1] primarily caused by tectonic forces compressing the Philippines into what geophysicists call the Philippine Mobile Belt. [2] Some notable Philippine faults include the Guinayangan, Masbate and Leyte faults.
Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by tectonic and localized stresses in Earth's crust. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relatively uniform lithology. The largest of these fault blocks are called crustal blocks.
A downthrown block between two normal faults dipping towards each other is a graben. A block stranded between two grabens, and therefore two normal faults dipping away from each other, is a horst. A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography.
With crustal extension, a series of normal faults which occur in groups, form in close proximity and dipping in opposite directions. [4] As the crust extends it fractures in series of fault planes, some blocks sink down due to gravity, creating long linear valleys or basins also known as grabens, while the blocks remaining up or uplifted produce mountains or ranges, also known as horsts.
Major physiographic elements of the Philippine Mobile Belt Puerto Princesa Subterranean River National Park marker describing the geologic history of the Philippines. In the geology of the Philippines, the Philippine Mobile Belt is a complex portion of the tectonic boundary between the Eurasian plate and the Philippine Sea plate, comprising most of the country of the Philippines.
The Marikina Valley fault system, also known as the Valley fault system (VFS), is a dominantly right-lateral strike-slip fault system in Luzon, Philippines. [2] It extends from Doña Remedios Trinidad, Bulacan in the north, running through the provinces of Rizal, the Metro Manila cities of Quezon, Marikina, Pasig, Taguig and Muntinlupa, and the provinces of Cavite and Laguna, before ending in ...
The 1975 M w 7.6 earthquake was caused by intra-slab normal faulting, while the 2012 M7.6 was a result of thrust faulting within the descending slab. [ 3 ] The relatively young Cotabato Trench subduction zone has been associated with several large megathrust earthquakes, including the 1918 Celebes Sea earthquake (M8.3), the 1976 Moro Gulf ...