   | |
| Local date | June 30, 1879 |
|---|---|
| Local time | 02:55 PST |
| Magnitude | 7.4 Mw |
| Epicenter | 9°48′N125°30′E / 9.8°N 125.5°E [1] |
| Type | Strike-slip |
| Areas affected | Philippine |
| Max. intensity | MMI X (Extreme) [2] |
The 1879 Surigao earthquake occurred on June 30 at 18:38 02:55 local time on the northeastern tip of Mindanao. The earthquake with a moment magnitude (Mw ) of 7.4 struck with an epicenter just south of Lake Mainit. Extensive damage occurred but there were no reports of casualties.
The Philippine Islands is situated in a highly deformed zone between the convergent boundary of the Eurasian and Philippine Sea plates, known as the Philippine Mobile Belt. Along the east, the Philippine Sea Plate subducts beneath the islands at the Philippine and East Luzon trenches. Major subduction complexes are also active along the southwestern coast of Mindanao at the Cotabato Trench and along the Manila Trench of the west Luzon.
Running through the Philippine Mobile Belt is the Philippine Fault System; a 1,200-kilometer-long, highly segmented strike-slip fault system. This left-lateral system of faults runs from southeastern Mindanao to northwestern Luzon. Strike-slip deformation within the Philippine Mobile Belt occurs as a result of oblique subduction of the Philippine Sea Plate, where the Philippine Fault System accommodates much of it. [3] The fault is seismically active and ruptures periodically in large earthquakes. Among the largest are the 1990 Luzon and 1973 Ragay Gulf earthquakes.
The earthquake ruptured approximately 100 km of the Philippine Fault System along the Surigao segment. The Surigao segment strikes in a slightly north-northeast orientation. Left-lateral stream offsets, and 1-meter-high scarps are evident that the fault is active. By studying the surface rupture length, a moment magnitude of 7.4 was estimated. [4] The reassessed magnitude is significantly larger than the previous value of 6.9 by Bautista and Okie in 2000. [1] [5]
It resulted in extreme shaking within the meizoseismal area, later assigned X (Extreme) on the modified Mercalli intensity scale. Using aerial photographs, a fault scarp was identified running the length from San Francisco, Surigao del Norte to Lake Mainit. The fault scarp was associated with the 1879 surface rupture. A maximum slip of 5 meters occurred at the surface. Further paleoseismology studies and trenching also identified fault scarps south of the lake. At least three other surface rupturing earthquakes occurred in the same segment during the last 1,300 years. [4]
Nearly all concrete infrastructures in Surigao, San Francisco, and Butuan were demolished. Ground failure, liquefaction, and subsidence occurred. Strong aftershocks occurred immediately after the mainshock. Spanish geologist Jose Centeno, appointed by the Governor-General of the Philippines measured up to 50 cm of subsidence of the ground after the earthquake. He reported many homes and trees were severely damaged; only three stone structures remained standing. Of the three, two buildings; one housing the governor and the other an administration office, suffered cracks on the walls and upper floors. A church constructed of thick coral limestone and reinforced with timber was seriously damaged. Wood, nipa, and bamboo-constructed homes were destroyed. In San Francisco, 26 of the 40 homes collapsed. The remaining homes that did not collapse were tilted over and most were eventually demolished for new constructions. Two bridges were also destroyed. [6]
The Manila Trench is an oceanic trench in the Pacific Ocean, located west of the islands of Luzon and Mindoro in the Philippines. The trench reaches a depth of about 5,400 metres (17,700 ft), in contrast with the average depth of the South China Sea of about 1,500 metres (4,900 ft). It is created by subduction, in which the Sunda Plate is subducting under the Philippine Mobile Belt, producing this almost N-S trending trench. The convergent boundary is terminated to the north by the Taiwan collision zone, and to the south by the Mindoro terrane. It is an area pervaded by negative gravity anomalies.
The 1990 Luzon earthquake occurred on July 16 at 4:26 p.m. (PDT) or 3:26 p.m. (PST) on the densely populated island of Luzon in the Philippines. The shock had a surface-wave magnitude of 7.8 and produced a 125 km-long ground rupture that stretched from Dingalan, Aurora to Kayapa, Nueva Vizcaya. The event was a result of strike-slip movements along the Philippine Fault and the Digdig Fault within the Philippine fault system. The earthquake's epicenter was near the town of Rizal, Nueva Ecija, northeast of Cabanatuan. An estimated 1,621 people were killed, most of the fatalities located in Central Luzon and the Cordillera region.
The 1976 Moro Gulf earthquake and tsunami occurred on August 17, 1976, at 00:11 local time near the islands of Mindanao and Sulu, in the Philippines. It measured 8.0 on the moment magnitude scale occurring at a depth of 20 km (12 mi). The earthquake was accompanied by a destructive tsunami that resulted in a majority of the estimated 5,000 to 8,000 fatalities. It was the deadliest and strongest earthquake in the Philippines in 58 years since the 1918 Celebes Sea earthquake.
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. It includes two subduction zones, the Manila Trench to the west and the Philippine Trench to the east, as well as the Philippine fault system. Within the Belt, a number of crustal blocks or microplates which have been shorn off the adjoining major plates are undergoing massive deformation.
The Philippine fault system is a major inter-related system of geological faults throughout the whole of the Philippine Archipelago, primarily caused by tectonic forces compressing the Philippines into what geophysicists call the Philippine Mobile Belt. Some notable Philippine faults include the Guinayangan, Masbate and Leyte faults.
The 1762 Arakan earthquake occurred at about 17:00 local time on 2 April, with an epicentre somewhere along the coast from Chittagong to Arakan in modern Myanmar. It had an estimated moment magnitude between 8.5 and 8.8 and a maximum estimated intensity of XI (Extreme). It triggered a local tsunami in the Bay of Bengal and caused at least 200 deaths. The earthquake was associated with major areas of both uplift and subsidence. It is also associated with a change in course of the Brahmaputra River to from east of Dhaka to 150 kilometres (93 mi) to the west via the Jamuna River.
The 1918 Celebes Sea earthquake occurred on August 15 at 12:18 UTC near the Moro Gulf coast of Mindanao. It had a magnitude of 8.3 on the moment magnitude scale and a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. It triggered a tsunami of up to 7 m in height and the combined effects of the earthquake and tsunami led to the deaths of 52 people.
The Bohol fault system is a reverse fault system in Bohol province, Philippines. This fault system contains three segments: the newly found North Bohol Fault following the 2013 Bohol earthquake, the South Offshore Fault, and the East Bohol Fault.
The 2017 Surigao earthquake occurred on February 10, 2017, at 10:03 PM (PST), with a surface-wave magnitude of 6.7 off the coast of Surigao del Norte in the Philippines. According to the PHIVOLCS earthquake intensity scale the earthquake was an Intensity VII (Destructive) earthquake at maximum. In the past Surigao province has been hit by a magnitude 7.2 tremor in both 1879 and 1893.
The subduction tectonics of the Philippines is the control of geology over the Philippine archipelago. The Philippine region is seismically active and has been progressively constructed by plates converging towards each other in multiple directions. The region is also known as the Philippine Mobile Belt due to its complex tectonic setting.
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The 1940 Shakotan earthquake occurred on August 2 at 00:08:22 JST with a moment magnitude (Mw ) of 7.5 and maximum JMA seismic intensity of Shindo 4. The shock had an epicenter off the coast of Hokkaido, Japan. Damage from the shock was comparatively light, but the accomanying tsunami was destructive. The tsunami caused 10 deaths and 24 injuries on Hokkaido, and destroyed homes and boats across the Sea of Japan. The highest tsunami waves were recorded at the coast of Russia while along the coast of Hokkaido, waves were about 2 m.
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