The 1879 Surigao earthquake occurred on June 30 at 18:38 02:55

local time Local time is the time observed in a specific locality. There is no canonical definition. Originally it was mean solar time, but since the introduction of time zones it is generally the time as determined by the time zone in effect, with daylight s ...

on the northeastern tip of

Mindanao Mindanao ( ) is the List of islands of the Philippines, second-largest island in the Philippines, after Luzon, and List of islands by population, seventh-most populous island in the world. Located in the southern region of the archipelago, the ...

. The earthquake with a

moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mwg, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. was defined in a 1979 paper ...

() of 7.4 struck with an

epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...

just south of

Lake Mainit Lake Mainit is the fourth largest lake in the Philippines, having a surface area of . The lake is also the deepest lake in the country with maximum depth reaching . It is located in the northeastern section of Mindanao and shared between the ...

. Extensive damage occurred but there were no reports of casualties.

Tectonic setting

The Philippine Islands is situated in a highly deformed zone between the

convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

of the Eurasian and Philippine Sea plates, known as the

Philippine Mobile Belt 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 ...

. Along the east, the Philippine Sea Plate

subducts Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second pla ...

beneath the islands at the

Philippine The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

and East Luzon trenches. Major subduction complexes are also active along the southwestern coast of Mindanao at the

Cotabato Trench The Cotabato Trench is an oceanic trench in the Pacific Ocean, off the southwestern coast of Mindanao in the Philippines. Along this trench the oceanic crust of the Sunda Plate beneath the Celebes Sea is being subducted beneath the Philippi ...

and along the

Manila Trench 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 , in contrast with the average depth of the South China Sea of about . It i ...

of the west

Luzon Luzon ( , ) is the largest and most populous List of islands in the Philippines, island in the Philippines. Located in the northern portion of the List of islands of the Philippines, Philippine archipelago, it is the economic and political ce ...

. Running through the Philippine Mobile Belt is the Philippine Fault System; a 1,200-kilometer-long, highly segmented

strike-slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

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. The fault is seismically active and ruptures periodically in large

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

s. Among the largest are the 1990 Luzon and

1973 Ragay Gulf earthquake The 1973 Ragay Gulf earthquake occurred at around 16:30 local time (UTC +8). It measured 7.4 and had a maximum intensity of IX (''Violent'') on the Modified Mercalli intensity scale. The Philippine Institute of Volcanology and Seismology assig ...

Earthquake

The

earthquake rupture In seismology, an earthquake rupture is the extent of slip that occurs during an earthquake in the Earth's crust. Earthquakes occur for many reasons that include: landslides, movement of magma in a volcano, the formation of a new fault, or, mos ...

d 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. The reassessed magnitude is significantly larger than the previous value of 6.9 by Bautista and Okie in 2000. It resulted in extreme shaking within the

meizoseismal area The meizoseismal area in an earthquake is the area of maximum damage. For example, in the Charleston, South Carolina, earthquake of 1886, the meizoseismal area was an area about twenty by thirty miles stretching northeast between Charleston and ...

, later assigned X (''Extreme'') on the

modified Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or ...

. Using aerial photographs, a

fault scarp A fault scarp is a small step-like offset of the ground surface in which one side of a fault has shifted vertically in relation to the other. The topographic expression of fault scarps results from the differential erosion of rocks of contrastin ...

was identified running the length from

San Francisco, Surigao del Norte San Francisco, officially the Municipality of San Francisco ( Surigaonon: Lungsod nan San Francisco; ), is a municipality in the province of Surigao del Norte, Philippines. According to the 2020 census, it has a population of 15,347 people. His ...

to Lake Mainit. The fault scarp was associated with the 1879

surface rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a Fault (geology), fault affects the Earth's surface. Surface rupture is opposed by buried rup ...

. A maximum slip of 5 meters occurred at the surface. Further

paleoseismology Paleoseismology is the study of ancient earthquakes using geologic evidence, such as geologic sediments and rocks. It is used to supplement seismic monitoring to calculate seismic hazard. Paleoseismology is usually restricted to geologic reg ...

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.

Impact

Nearly all concrete infrastructures in Surigao, San Francisco, and

Butuan Butuan (pronounced ), officially the City of Butuan (; Butuanon: ''Dakbayan hong Butuan''; ), is a highly urbanized city and the regional center of Caraga, Philippines. It is the '' de facto'' capital of the province of Agusan del Norte ...

were demolished. Ground failure, liquefaction, and subsidence occurred. Strong

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...

s occurred immediately after the

mainshock In seismology, the mainshock is the largest earthquake in a sequence, sometimes preceded by one or more foreshocks, and almost always followed by many aftershocks. Foreshock A foreshock is an earthquake that occurs before a larger seismic ev ...

. Spanish

geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...

Jose Centeno, appointed by the

Governor-General of the Philippines The governor-general of the Philippines (; ; ) was the title of the Executive (government), government executive during the colonial period of the Philippines, first by History of the Philippines (1521–1898), the Spanish in Mexico City and l ...

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.

References

{{Earthquakes in the Philippines Earthquakes in the Philippines 1879 in the Philippines 1879 earthquakes 1879 in the Spanish Empire History of Surigao del Norte History of Dinagat Islands 1870s disasters in Asia 19th-century disasters in the Philippines

Tectonic setting

Earthquake

Impact

See also

References