Idosawa Fault
Encyclopedia
The is an active earthquake
fault with a length of 8 mi (13 km), located in Fukushima Prefecture
of Japan
, to the west of Iwaki city
. It mainly consists of a trace of three striations
. Although the Idosawa Fault primarily behaves as a normal dip-slip fault, it also consists of a north-trending component described as a right-lateral strike-slip fault. The main structural trend is north-northwest–south-southeast, with sinking observed only to the south on the east side of the fault. Metamorphic rock
and Cretaceous
strata
, as well as granite
and epidiorite are distributed in the region; the fault is described as a limit to the distribution of tuff
from the Neogene Period
.
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
fault with a length of 8 mi (13 km), located in Fukushima Prefecture
Fukushima Prefecture
is a prefecture of Japan located in the Tōhoku region on the island of Honshu. The capital is the city of Fukushima.-History:Until the Meiji Restoration, the area of Fukushima prefecture was known as Mutsu Province....
of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, to the west of Iwaki city
Iwaki, Fukushima
is a city located in the southern part of the Hamadōri coastal region of Fukushima Prefecture, Japan.A designated "core city", Iwaki is also one of the growing number of hiragana cities. Its area is 1,231.35 km², making it the 10th largest city in Japan...
. It mainly consists of a trace of three striations
Striation (geology)
In geology, a striation means linear furrows generated from fault movement; The striation's direction reveal the movement directions in the fault plane. Similar striations can occur with glaciation....
. Although the Idosawa Fault primarily behaves as a normal dip-slip fault, it also consists of a north-trending component described as a right-lateral strike-slip fault. The main structural trend is north-northwest–south-southeast, with sinking observed only to the south on the east side of the fault. Metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
, as well as granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
and epidiorite are distributed in the region; the fault is described as a limit to the distribution of tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
from the Neogene Period
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
.
Notable earthquakes
- March 19, 2011: A magnitude 6.1 struck near Ibaraki PrefectureIbaraki Prefectureis a prefecture of Japan, located in the Kantō region on the main island of Honshu. The capital is Mito.-History:Ibaraki Prefecture was previously known as Hitachi Province...
, with its hypocenterHypocenterThe hypocenter refers to the site of an earthquake or a nuclear explosion...
located near the Idosawa Fault. The earthquake occurred as a result of normal-faulting. - March 23, 2011: A magnitude 6.0 earthquake struck near northern Ibaraki. The quake occurred near the fault, with a focal mechanism of a normal-fault type.
- April 11, 2011: A magnitude 6.6 earthquakeApril 2011 Fukushima earthquakeThe was a potent magnitude 6.6 Mw intraplate aftershock that occurred at 17:16 JST on Monday, 11 April 2011. With a shallow focal depth of 10 km , it was centered inland about 36 km west of Iwaki, Japan, resulting in widespread moderate to localized strong shaking...
with a depth of 6 mi (10 km) struck near Ishikawa, FukushimaIshikawa, Fukushimais a small market town located in Ishikawa District, Fukushima, Japan.During World War II, the town had a secret uranium mine for the Japanese atomic bomb project....
. The quake occurred along the fault and caused a surface rupture of near 4 mi (7 mi). In addition, a vertical displacementVertical displacementIn tectonics, vertical displacement is the shifting of land in a vertical direction, resulting in a permanent change in elevation.Two types of vertical displacement are uplift, an increase in elevation, and subsidence, a decrease in elevation....
of 0.8–1.8 m was observed.