Earthquakes in Mongolia

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343
The cumulative number of earthquakes around Ulaanbaatar

The seismic activity of Mongolia is associated with the deformation induced by the world’s largest collision of tectonic plates between Indian and Eurasian.

Research papers of scientists Tapponnier, Molnar, Baljinnyam, Schlupp, and Bayasgalan, which were published from 1979 to 1999, indicated that Mongolia is situtated at the transition point between the Eurasia-Indian collision and extensive tectonic structures in the northern regions of the country, particularly in Khuvsgul area and Baikal Rift Zone.

Unlike earthquakes that occur along tectonic plate boundaries, continental earthquakes are widely distributed over large regions and typically have shallow depths, in the range of 10 to 25 km beneath the surface. Major continental earthquakes usually occur along seismically active faults, which individually have very long recurrence intervals in the range of several thousand years.

Late Quaternary deformation in Mongolia is distributed over a vast region, and includes a full spectrum of deformation styles and structural orientations. In the north, the activity is dominated by the Baikal Rift Zone and Khuvsgul, Busiin River and Darkhad grabens with a transfer zone following the Tunka Basin.

In the west, the activity is related to the deformation of the Altai range, characterized mainly by right-lateral strike-slip motion. The occurrence and distribution of strong earthquakes are the manifestation and result of these widespread and varied styles of deformation. Over the 20th century, the four most powerful recorded earthquakes with Mw (Moment Magnitude) more than eight occurred in Mongolia on July 9, 1905; July 23, 1905; August 10, 1931; and December 4, 1957.

The locations of earthquakes, especially large earthquakes, are not uniformly and randomly distributed, rather they cluster on several faults of prominent late Quaternary tectonic activity. In the Altai range, the observed activity is mainly concentrated at its northern part and along the fault which ruptured in 1931 during Fu Yun Earthquake, which was measured at eight Mw. The Institute of Astronomy and Geophysics (IAG) of Mongolian Academy of Sciences recorded many small events along this fault, 73 years after the Fu Yun Earthquake.

Between Darkhad basin and Altai range, the activity is mainly focused along the faults that ruptured in 1905 during an eight Mw earthquake that occurred on July 9, 1905 in Tsetserleg soum of Khuvsgul Province and an 8.4 Mw earthquake on 23 July 1905 in Bulnai range, Zavkhan Province. At the southern end of Altai range, seismic activity is mainly associated to the Takhiin Shar earthquake, which occurred on July 4, 1974. More to the east, in the Govi-Altai range, the main activity is associated with the eight Mw Bogd earthquake that occurred on December 4, 1957, and its aftershocks.

The seismic activities between the Altai range and Darkhad are associated with the seven Mw earthquake that occurred in Mogod soum of Bulgan on January 5, 1967. Outside these areas of high seismic activity, the seismicity is mainly widespread in wide ranges of areas. Note the low seismicity inside the Khangai Dome due to the plate deformation of this region.

Researcher M.Ulziibat discovered in 2006 that a large disturbance measured at 7.3 Mw occurred in the northern part of Altai, in Russia on September 27, 2003.
Nevertheless, the seismic activity observed in the last century occurred in places of potential earthquake. For example, the Khangai Dome was an earthquake prone area 300 to 500 years ago.

Researcher Khilko found a large fracture in the central area of Khangai in 1985 and concluded that it might have been caused by a magnitude seven earthquake in 1570.

 
SEISMIC ACTIVITY IN ULAANBAATAR

 
The seismic activity in and around Ulaanbaatar is relatively low. According to the Seismic zoning map of Mongolia, published in 1983, nearly 75 percent of Mongolia’s territory lies in the seismic intensity zone with magnitude seven or more. Most active zones in Ulaanbaatar are Sonsoglon, Emeelt and Songino areas, approximately 20 km west of the city center.

Several seismic activities have been recorded in this area from 2000 to 2016. During this period, the IAG has detected 11,178 events with magnitudes ranging from 0.1 to 5.2.

The IAG detected six earthquakes near Ulaanbaatar in recent years:

 
December 3, 2005: 5.1 Mw earthquake was detected in Lun soum, Tuv Province

• March 22, 2009: 4.1 Mw earthquake was detected near Undur Davaa, Sergelen soum in Tuv Province

• October 14, 2013: 3.8 Mw earthquake was detected near Emeelt area in western Ulaanbaatar

• October 3, 2015: 4.4 Mw and 3.8 Mw earthquakes were detected in Shariin Khooloi of Uliastai valley, Bayanzurkh District.

• October 10, 2015: 4.7 Mw earthquake was dectected in Batsumber soum, Tuv Province.

 
IAG researcher D.Ankhtsetseg pointed out that the IAC has done several geophysical and paleoseismic studies around Ulaanbaatar and its surrounding areas. A team of international scientists found several quaternary active faults in Khustai, Avdar, Emeelt, Gunj, Sharkhai, and Mungunmorit near Ulaanbaatar.

The most recent seismic activities near Ulaanbaatar are associated with active fault zones in Khustai, Emeelt, Gunj, and Deren. The IAC has most recently recorded seismic activity near the Tavan Tolgoi mine and Tsogttsetsii soum of Umnugovi Province.

A magnitude 3.3 earthquake occurred in the area on December 2, 2016 at 09:38 a.m. Residents of Tsogttsetsii soum and Tavan Tolgoi mine workers reported that they could feel the earthquake.

The IAC confirmed that 62 aftershocks with magnitudes 0.5 to 3.7 were detected in the following eight days. In particularly, the strongest aftershock occurred on December 3, 2016. A second earthquake, with magnitude 3.8, occurred on February 2 at 10:00 p.m. in the Tavan Tolgoi area.

Sixteen aftershocks followed the second earthquake, reported the IAC. No reports of damages and losses have been made in relation to the earthquakes in Tavan Tolgoi area. Locals speculated that the earthquakes might have been caused by mining activities such as underground blasting. The IAC said it is still studying the event and that so far no connections have been made to mining activities.

The IAC noted that seismic activity detection in the region is poor and that more needs to be invested in this area. Since an earthquake occurred in the beginning of 2010 in Deren soum of Dundgovi Province, which was felt by Ulaanbaatar’s residents following the 2010 Haiti earthquake, President Ts.Elbegdorj started to focus on preventing earthquake hazards and started a campaign to increase public awareness. The National Emergency Management Agency and the IAC have been working closely in recent years to reduce disaster related risks.

Director of the IAC S.Demberel said that Deputy Prime Minister and Head of the National State Emergency Commission U.Khurelsukh is actively working to strengthen discipline and responsibilities of state officials in charge of disaster management. He pointed out that preparation is essential for addressing risks related to natural disasters such as earthquakes, and underlined that it can dramatically reduce losses and damages.

The Disaster Risk Reduction Center was established in Ulaanbaatar to educate the public on disaster response and management. President Ts.Elbegdorj put forward a bill on disaster response, which hopes to bolster disaster response, give responsibilities and duties to emergency management authorities, strengthen discipline, systematic risk reduction measures, and enhance the legal and regulatory environment for providing humanitarian assistance in the event of a disaster. Parliament has supported further discussion of the bill.

The government and the United Nations Office for Disaster Risk Reduction will jointly organize the 2018 Asian Ministerial Conference on Disaster Risk Reduction in Ulaanbaatar.

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