A foreshock is an earthquake that occurs before a larger seismic event and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the full sequence of events has happened.
The 2004 Al Hoceima earthquake occurred on 24 February at 02:27:47 local time near the coast of northern Morocco. The strike-slip earthquake measured 6.3 on the moment magnitude scale and had a maximum perceived intensity of IX (Violent) on the Mercalli intensity scale. Between 628 and 631 people were killed, 926 were injured, and up to 15,000 people were made homeless in the Al Hoceima-Imzourene-Beni Abdallah area.
The 1946 Dominican Republic earthquake occurred on August 4 at 17:51 UTC near Samaná, Dominican Republic. The mainshock measured 7.8 on the moment magnitude scale and 8.1 on the surface wave magnitude scale. An aftershock occurred four days later on August 8 at 13:28 UTC with a moment magnitude of 7.0. A tsunami was generated by the initial earthquake and caused widespread devastation across Hispaniola. The tsunami was observed in much of the Caribbean and the northwestern Atlantic Ocean.
The 2002 Denali earthquake occurred at 22:12:41 UTC November 3 with an epicenter 66 km ESE of Denali National Park, Alaska, United States. This 7.9 Mw earthquake was the largest recorded in the United States in 37 years. The shock was the strongest ever recorded in the interior of Alaska. Due to the remote location, there were no fatalities and only one injury.
The 1202 Syria earthquake struck at about dawn on 20 May 1202 with an epicenter in southwestern Syria. The earthquake is estimated to have killed around 30,000 people. It was felt over a very wide area, from Sicily to Mesopotamia and Anatolia to upper Egypt, mostly affecting the Ayyubid Sultanate and the Kingdom of Jerusalem. The cities of Tyre, Acre and Nablus were heavily damaged. A magnitude of 7.6 has been estimated with damage up to XI on the Mercalli intensity scale.
The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time on 15 October just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California. The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at US$30 million. The irrigation systems in the Imperial Valley were badly affected, but no deaths occurred. It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier.
The 1969 Sharm El Sheikh earthquake occurred on March 31 off the southern Sinai Peninsula in northeastern Egypt. The epicenter was located near Shadwan island, southwest of the city of Sharm El Sheikh, at the confluence of the Red Sea and the Gulf of Suez. This normal-slip shock measured 6.6 on the moment magnitude scale, had a maximum reported intensity of VII on the Mercalli intensity scale, and was responsible for several deaths and injuries.
The 2014 Murmuri earthquake occurred on August 18 in the Zagros Mountains of Iran with a moment magnitude of 6.2 and a maximum Mercalli intensity of VIII (Severe). The thrust earthquake injured 60–330 people and was followed by a number of high intensity aftershocks.
The 1912 Maymyo earthquake or Burma earthquake struck Burma on the morning of May 23, with an epicentre near Taunggyi and Pyin Oo Lwin in Shan State. The earthquake was initially calculated at 8.0 on the surface wave magnitude scale (Ms ) by Beno Gutenberg and Charles Francis Richter, and described by them as being one of the most remarkable seismic events in the early 1900s. Recent re-evaluation of the earthquake, however, have revised the magnitude to 7.6–7.9. It was preceded by two foreshocks on May 18 and 21 with respective intensities V and VII on the Rossi–Forel scale, while the mainshock was assigned IX. Shaking was felt throughout most of Burma, parts of Siam and Yunnan; an area covering approximately 375,000 square miles. It was one of the largest earthquakes in the country.
The 1987 Superstition Hills and Elmore Ranch earthquakes were a pair of earthquakes measuring Mw 6.0 and 6.5 that rattled the Imperial Valley of California. The earthquakes caused damage in Southern California and Mexico, but was limited due to their location in a sparsely populated area. It was felt as far as Las Vegas and Phoenix. More than 90 were injured, and two people were killed in Mexico.
In 1954, the state of Nevada was struck by a series of earthquakes that began with three magnitude 6.0+ events in July and August that preceded the Mw 7.1–7.3 mainshock and M 6.9 aftershock, both on December 12. All five earthquakes are among the largest in the state, and the largest since the Cedar Mountain earthquake of 1932 and Pleasant Valley event in 1915. The earthquake was felt throughout much of the western United States.
On January 1, 1996, at 4:05 p.m. Central Indonesia Time, an earthquake with an epicenter in the Makassar Strait struck north of Minahasa on the island of Sulawesi, Indonesia. The earthquake measured 7.9 on the moment magnitude scale and was centered off Tolitoli Regency in Central Sulawesi, or 25 km from the Tonggolobibi village. A tsunami of 2–4 m (6.6–13.1 ft) was triggered by this earthquake as a result. At least 350 buildings were badly damaged, nine people died and 63 people were injured.
The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST, near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). Damage was relatively moderate, and the mainshock was assigned a maximum Modified Mercalli intensity (MMI) of VII. Shaking was felt in Nevada, and Arizona. It was the largest earthquake to strike California since 1952, and its display of afterslip became the subject of scientific interest.
On January 30, 1973, at 15:01 (UTC–6), a magnitude 7.6 earthquake struck 35.3 km (21.9 mi) beneath the Sierra Madre del Sur range in the Mexican states of Colima, Jalisco and Michoacán. On the Mercalli intensity scale, the earthquake reached a maximum intensity of X (Extreme), causing serious damage in the region. At least 56 people were killed and about 390 were injured. The event is commonly referred to as the Colima earthquake.
The 1979 Ghaenat earthquakes were a series of large earthquakes in Qaen County, Khorasan Province, northeast Iran, near the Afghanistan border. The first mainshock, known as the Korizan earthquake with a surface wave magnitude (Ms ) of 6.6 and moment magnitude (Mw ) of 6.8, struck on November 14, while the Ms 7.1 or Mw 7.2 Koli-Boniabad earthquake struck on November 27. The two mainshocks were assigned a maximum Modified Mercalli intensity of VIII (Severe) and X (Extreme), respectively. The earthquakes caused extensive damage throughout northeastern Iran, killing an estimated 297 to 440 people and left at least 279 injured.
On December 5, 1456, the largest earthquake to occur on the Italian Peninsula struck the Kingdom of Naples. The earthquake had an estimated moment magnitude of Mw 7.19–7.4, and was centred near the town of Pontelandolfo in the present-day Province of Benevento, southern Italy. Earning a level of XI (Extreme) on the Modified Mercalli intensity scale, the earthquake caused widespread destruction in central and southern Italy. An estimated 30,000–70,000 people were killed. It was followed by two strong Mw 7.0 and 6.0 earthquakes to the north on December 30.
The 1915 Imperial Valley earthquakes were two destructive shocks centered near El Centro, California on June 22. The earthquakes measured 6.25 and occurred nearly one hour apart at 19:59 and 20:57 PST. Both shocks were assigned VIII (Severe) on the Modified Mercalli intensity scale. Heavy damage occurred in the areas of Mexicali and El Centro, amounting to $900,000. At least six people were killed in the earthquakes.
The 1997 Bojnurd earthquake occurred on 4 February at 14:07 IRST in Iran. The epicenter of the 6.5 earthquake was in the Kopet Dag mountains of North Khorasan, near the Iran–Turkmenistan border, about 579 km (360 mi) northeast of Tehran. The earthquake is characterized by shallow strike-slip faulting in a zone of active faults. Seismic activity is present as the Kopet Dag is actively accommodating tectonics through faulting. The earthquake left 88 dead, 1,948 injured, and affected 173 villages, including four which were destroyed. Damage also occurred in Shirvan and Bojnord counties. The total cost of damage was estimated to be over US$ 30 million.
The 1979 Saint Elias earthquake occurred near noon local time on the 28th of February. It measured Mw 7.4–7.6. Though the maximum recorded Modified Mercalli intensity was VII, damage was minimal and there were no casualties due to the remoteness of the faulting. The epicenter lies near the Alaskan border between America and Canada.
The 1977 Bob–Tangol earthquake struck Kerman province of Iran on December 19 at 23:34 GMT. The earthquake destroyed homes and left thousands homeless. A maximum Modified Mercalli intensity of VII was evaluated based on damage. Between 584 and 665 people perished while a further 500–1,000 were injured. Casualties from the earthquake was considered moderate due to the sparsely populated area it affected. The earthquake measured 5.9 and struck at a depth of 22.7 km (14.1 mi). It had a strike-slip focal mechanism, which was unusual as the source structure was a thrust fault. It was part of a sequence of strong earthquakes along the 400 km (250 mi) Kuh Banan Fault. Preceded by foreshocks the month before, many residents became wary of a larger earthquake and took refuge outside their homes, contributing to the moderate death toll. However, there were none immediately before the mainshock so many were still in their homes when it struck. Aftershocks were felt for several months, some causing additional damage.
