The possibility of tsunamis in Vietnam

The last 7.1-Ritchter earthquake on December 26, 2006 in Taiwan, followed by a tsunami warning disturbed and worried Vietnamese coastal residents. Although a 0.8 m high wave was recorded at the Quy Nhon metering station according to the announcement of the Geophysical Institute, there was no further notice of the occurrence of a tsunami, even if it was small, along the coast of Vietnam. We try to understand the mechanism of occurrence of tsunamis and their occurrence in the coastal areas of Vietnam.

So far there can be at least four activities on the earth's shell that can form tsunamis: the impact of a sea-surface meteorite; activities of underground volcanoes on the sea; slipping, land slides on the sea; and activities that move the crust along collapsing or collapsing systems.

Evidence of the impact of a meteorite in Southeast Asia is determined by the presence of tektites (www.austmus.gov.au/geoscience/tektites/index.htm) which are splinters that burst out when meteorites rush into the earth, scattered in a large area. In Vietnam, tektites are found more in Lam Dong, Binh Thuan and some places in the North. In Laos, tektites are found in Muong Nong . These tektites are called by their own names depending on the area they were found: Indochinites for Indochina, Philippines for the Philippines .

Suevite (5 cm x 3 cm). Ries Crater, Bavaria, Germany. (Photo: © Australian Museum)

The age of these tektites was determined by the Ar / K radioisotope method of 600,000 to 700,000 years and the meteorite collision location in Southeast Asia, yet to be determined, although some houses The geology suggests that the Tonle Sap Lake (Cambodia) may be the result of this collision. The tsunami caused by this collision result will of course be a terrible disaster. However, the transport is not a thousand years, but a few hundred thousand years, this one may not bother us much.

Fire paint exploding on the sea floor will also create a tsunami. Krakatoa volcano, Indonesia exploded in 1883, followed by a tsunami that hit the shore, ravaged over 167 villages and claimed 36,417 lives. This is a kind of fire paint established in the form of tectonic submergence zone (subduction zone), fire painted with silicon-rich lava, so thick that there is an intense and devastating activity, the pattern still exists day by day. now in Indonesia, Philippines, Japan . We still have the presence of fire on the mainland, although it has stopped working (Pleiku, Long Khanh - Dong Nai .), and on the sea of ​​Tro Tro (1923) Quy Nhon offshore. Fortunately, this is a kind of peaceful fire paint, with dilute lava, type of establishment where ant cracked (rift zone), so do not create explosive forms when operating and difficult to cause tsunamis as soon as they are works on the sea.

Direction is likely to appear tsunamis in Vietnam

Land slides with a large hill slide down to the lower area due to regional earthquakes, or other natural or artificial agents. Similarly, on the sea floor, a large area of ​​land could collapse, crash into the lower side and thus cause tremors in the seabed and cause tsunamis. The topography of the central coast of Vietnam is an abruptly high elevation to a low-lying terrain of Quy Nhon, running along the north-south coast. The phenomenon of land on the sea so it is very possible to follow the seismic activities that we have seen that happened on the mainland (Dien Bien) or on the sea (Vung Tau) in recent years. The tsunami caused by this activity has not recorded much damage, but for Vietnam it is difficult to detect as well as prevention because they have a position near the shore so it will spread to The land is very fast, once established.

Tsunami caused by seismic activities is the type of tsunami recorded to cause the most devastation and death, but it should be differentiated that only a few seismic types are capable of causing tsunamis and unique only when they happen on the sea. Earthquakes occurred when two blocks of plates (plates) suddenly slid side by side (fault plane). There are two types of normal and thrust - in the vertical space - that can cause tsunamis, if this movement occurs in the seabed they will push up or pull down a huge amount of water and agitation causes tsunamis. Strike-slip type almost completely does not cause tsunamis even if they occur on the sea.

Phuket Wild Tan (Thailand) in 2004

The following image is the result of recording a magnitude greater than 6 Ritchter degrees and the location of seismic centers between 12.2000 and 12/2006 by IRIS (Incoroperated Research Institution for Seismology - http:/// www .iris.edu) in Southeast Asia. A bit of expertise in the field of geology, all kinds of seismic places here belong to the group generated from the activity of pushing up or falling down - the kind that is most likely to cause tsunamis - where the interface of the two regions . However, the key point is that the relative geographical position of the geographic areas is the determining point for the affected and devastated areas of tsunamis if they are established.

South, southwest and west Indonesia is an area in which Australia / India Sea Plate (Australia / India Sea Plate) sinks beneath the Sundaland Plate and causes volcanoes (Krakato, 1883) with tsunamis (Bada Aceh , 2004). In the context of geography, tsunamis, if occurring in this region, will develop towards the Australian sea or the Indian Sea south or southwest. The South China Sea to the north, is protected by large ranges of Indonesia, Malaysia and Borneo so it can be said that Vietnam is completely assured if tsunamis occur in this area.

To the east, the Pacific Ocean shell sinks beneath Sundaland, once again earthquakes and tsunamis are likely to occur along the south up to the eastern edge of the southern part of the Philippines. When tsunamis occur in this region, Vietnam will be shielded by the Philippines, tsunamis hardly have the opportunity to penetrate the South China Sea and affect Vietnam.

In the north, in the northern Philippines and southern Taiwan, China sea shells collapse beneath the Philippine sea shell and cause earthquakes to develop toward the South China Sea, which is a tectonic motion that can cause tsunamis. and affect Vietnam. We can see once again, with the shielding of Hainan Island, the northern part of Vietnam is likely to be safer than central and southern Vietnam if the tsunami occurs.

In short, we can safely not worry about the possibility of tsunamis caused by volcanic activity on the East Sea. We may have to accept fate if the disaster of a meteor crashed into the Earth's crust in the South China Sea, the opportunity is not a thousand years but every few hundred thousand years. Although cross-border races in Vietnam's territory are believed to be inactive, recent earthquakes in the Dien Bien Phu area show the Red River and their extension on the East Sea, Quy Nhon, off the domain. Trung is still active.

Sri Lanka's fallow in 2004

Similarly, earthquakes off the coast of Vung Tau may be evidence of the reactivation of Wang Chao in southern Vietnam. These earthquakes are small and not a model to create tsunamis, but indirectly they can arouse collapses on the sea and cause tsunamis. The threat of tsunamis that have the opportunity to affect Vietnam will come from Taiwan and the northwest of the Philippines, when seismic events take place here. It is necessary to work closely with international agencies and research institutes in the region to promptly warn tsunamis if they occur, whenever an earthquake occurs in this region.

After all, there is a need for studies on Ancient Tsunami (Paleotsunami), these studies have been available in Indonesia, Malaysia and the Philippines . but hardly noticed in Vietnam, to find evidence, the intensity and frequency of tsunamis in the past, to take appropriate measures to respond.

Dr. Nguyen Anh Tuan - San Jose State University (USA)