Purpose
The main scientific goal of the centre is the definitive compilation of earthquake information and the readings on which they are based. Collection of reports of earthquake effects is also an important part of its operation and the Centre recomputes the location and occurrence time of earthquakes worldwide, making use of all available information.
Since 1957 the manipulation of the large volume of data has been mainly carried out by computer. Up until then ISS locations were determined manually with the help of a large globe. The ISC now uses a network of workstations accessing a relational database of nearly 50 Gbytes of online data.
The analysis of the earthquake data is undertaken in monthly batches and begins after at least 18 months to allow the information used to be as complete as possible. Although much of the work would be impossible without the centre's large suite of computer programs, the final editing of events large enough to be detected by several independently operated networks is always carried out by seismologists who scrutinise the output for unlikely events and chance misassociation of readings.
During analysis the computer program first groups origin estimates from different agencies and then associates the individual station readings with the most likely event. In a typical month more than 200,000 station readings are analysed leading to an average of 10,000 events per month being identified, of which some 4,000 require manual review. Misassociations and other discrepancies are rectified and the remaining unassociated readings are searched for new events and previously unreported earthquakes are added to the database. The total number of events listed each month is several times greater than those obtained by any other worldwide location service and results from ISC's goal to provide a fully comprehensive list.
The 1978 Tabas earthquake occurred on September 16 at 19:05:55 local time in central Iran. The shock measured 7.4 on the moment magnitude scale and had a maximum Mercalli intensity of IX+ (Violent). The death toll was in the range of 15,000–25,000, with severe damage occurring in the town of Tabas. The day before, a 5.5 magnitude quake had struck southwestern Iran in the morning and killed at least 42 people in and around the towns of Masjid-e Solaiman and Izeh.
The 1976 Songpan–Pingwu earthquake that struck Songpan and Pingwu counties in Sichuan, China consisted of three mainshocks on the 16th, 21st, and 23rd (UTC) of August. A 1984 report gave the magnitudes as 7.2, 6.7, and 7.2, respectively. The magnitudes were subsequently recalculated as 6.7, 6.3, and 6.4 on the scale, and 7.0, 6.6, and 6.7 on the scale. These were preceded by an earthquake swarm lasting three years. During the period from August 16 to August 31 there were over 400 aftershocks of magnitude 3.0 or greater.
The 2008 Iceland earthquake was a doublet earthquake that struck on 29 May at 15:46 UTC in southwestern Iceland. The recorded magnitudes of the two main quakes were 5.9 and 5.8 Mw , respectively, giving a composite magnitude of 6.1 Mw . There were no human fatalities, but injuries were reported and a number of sheep were killed. The epicenter of the earthquake was between the towns of Hveragerði and Selfoss, about 45 kilometers (28 mi) east-southeast of the capital, Reykjavík. It was the strongest earthquake to hit Iceland since the summer of 2000.
The 2009 West Papua earthquakes occurred on January 4 local time in Indonesia's Tambrauw Regency in Southwest Papua. The very large earthquake doublet comprised a 7.6 initial shock that had a maximum Mercalli intensity of VI (Strong) and a second event measuring Mw 7.4 and a maximum Mercalli intensity of VII. The events took place less than three hours apart to the east-northeast of Sorong on the Bird's Head Peninsula and left at least four people dead and dozens injured.
In the early morning hours of August 16, 1931, a powerful earthquake occurred in West Texas with a maximum Mercalli intensity of VIII (Severe). Estimates of its magnitude range between 5.8 and 6.4 mb, making it the most powerful earthquake ever recorded in Texas history. Its epicenter was near the town of Valentine, Texas; there, the earthquake caused damage to many homes and buildings. The earthquake may have been caused by movement along oblique-slip faulting in West Texas, the most seismically active region in the state. Shaking from the earthquake was perceptible within a 400 mi (640 km) radius of the epicenter, affecting four U.S. states and northern Mexico. Several foreshocks and aftershocks accompanied the primary temblor, with the aftershocks continuing until at least November 3, 1931. The main earthquake caused no fatalities, though several people sustained minor injuries; the damage in Valentine amounted to $50,000–$75,000.
The 1995 Neftegorsk earthquake occurred on 28 May at on northern Sakhalin Island in the Russian Far East. It was the most destructive earthquake known within the current state of Russia, with a magnitude of 7.1 and maximum Mercalli intensity of IX (Violent) that devastated the oil town of Neftegorsk, where 1,989 of its 3,977 citizens were killed, and another 750 injured.
The 1967 Mudurnu earthquake or more correctly, the 1967 Mudurnu Valley earthquake occurred at about 18:57 local time on 22 July near Mudurnu, Bolu Province, north-western Turkey. The magnitude 7.4 earthquake was one of a series of major and intermediate quakes that have occurred in modern times along the North Anatolian Fault since 1939.
The 2010 Mindanao earthquakes occurred in the southern Philippines in the Moro Gulf. This was a complex sequence of events including three main events of magnitude 7.3 or greater on the 23rd of July, and two significant aftershocks of magnitude 6.6 on the 24th and 29th. All of these were deep focus earthquakes, at depths from 565 km (351 mi) to 634 km (394 mi). This resulted in minimal, but very widespread shaking at the surface, with a maximum intensity of IV on the PEIS scale; consequently there were no reports of casualties or damage.
The 1997 Cariaco earthquake occurred on July 9 at with a moment magnitude of 6.9 and a maximum Mercalli intensity of VIII (Severe). With its epicenter near Cariaco, Venezuela, at least 81 people were killed and over 500 were injured. Disruption of power, telephone, and water services was reported. This earthquake was felt in much of northeastern Venezuela and could also be felt in Trinidad and Tobago. This earthquake was on the strike-slip El Pilar Fault.
The 1953 Torud earthquake occurred at the northeastern border of the Great Salt Kavir in Torud, Semnan, Iran on 12 February. The shock had a moment magnitude of 6.6 and had a maximum Mercalli intensity of VIII (Severe). At least 800 people were killed.
The 1943 Alahan Panjang earthquakes occurred on June 8 and June 9 UTC in Sumatra, then under Japanese occupation. This was an earthquake doublet.
The 1990 Vrancea earthquakes were three earthquakes on 30 and 31 May 1990 with magnitudes of 7.0 and 6.2 Mw that struck the Romanian county of Vrancea, on two consecutive days. Severe damage in the Bucharest-Brăila-Brașov area was reported and dozens of casualties in Romania and neighbouring Moldova, Ukraine and Bulgaria.
The 1989 Chenoua earthquake occurred on October 29 at in northern Algeria. The dip-slip event had a moment magnitude of 5.9 and a maximum Mercalli intensity of VIII (Severe). At least 22 were killed and many were injured with total losses of $5 million.
The 1976 Sabah earthquake occurred at 10:56 am on 26 July near Lahad Datu in the eastern portion of Sabah, Malaysia. The moment magnitude 6.3 earthquake is one of the strongest in Malaysia to be recorded by seismic instruments. It had a focal mechanism corresponding to strike-slip faulting. While slightly larger than the 2015 Sabah earthquake, the 1976 event caused less extensive damage, in the form of cracks on several buildings and ground cracks.
The 1974 Lesser Antilles earthquake occurred at on October 8 with a moment magnitude of 6.9 and a maximum Mercalli intensity of VIII (Severe). Four people were injured in what the United States' National Geophysical Data Center called a moderately destructive event.
The 1977 Tonga earthquake took place on 23 June at some 200 km southwest of Tongatapu, with shocks affecting all islands of the kingdom of Tonga. The earthquake measured 8.0 on the moment magnitude scale and had a maximum intensity of VIII (Severe) on the Mercalli intensity scale.
The 1976 Longling earthquake in Yunnan Province, People's Republic of China, was a doublet earthquake, with two main shocks striking just east of Longling at 12:23:20 and 14:00:22 UTC. The magnitudes were estimated at 6.7 and 6.6, respectively, on the (GCMT) scale, and 6.9 and 7.0 on the scale; Chinese sources put these at 7.4 and 7.3 on the scale. The region is noted for the quantity and intensity of its earthquakes, and the complexity of its tectonics, which are closely related to the collision between the Indian and Eurasian tectonic plates.
The 1982 Ometepec earthquake that struck Mexico's southwestern coast near Ometepec (Guerrero) on 7 June was a doublet earthquake that ruptured in two steps. The first happened at 06:52 UTC, the second five hours later at 10:59 UTC. Estimated magnitudes are 6.9 and 7.0 on the scale, and 5.8 and 6.0 on the scale. The maximum Mercalli intensities were VII and VIII, respectively.
On April 13, 1923, at 15:31 UTC, an earthquake occurred off the northern coast of the Kamchatka Peninsula in the USSR, present-day Russia. The earthquake had a surface-wave magnitude (Ms ) of 6.8–7.3 and an estimated moment magnitude (Mw ) of 7.0–8.2. This event came just two months after a slightly larger earthquake with an epicenter struck south of the April event. Both earthquakes were tsunamigenic although the latter generated wave heights far exceeding that of the one in February. After two foreshocks of "moderate force", the main event caused considerable damage. Most of the 36 casualties were the result of the tsunami inundation rather than the earthquake.
