Dangerous earthquake in Vietnam

The earthquake on 16.5 did not cause any significant damage but it caused panic among thousands of people working in high-rise buildings in Hanoi. So is Vietnam at risk of earthquakes? From the US, Dr. Nguyen Anh Tuan sent an article about collaboration with Thanh Nien , please post with readers.

The earth shell is composed of geographical areas (India plate, Eurasia plate, North America plate .) located adjacent and moving in different directions with the speed of several centimeters per year. As they move, they can stumble into each other, an array will sink under the other plate, or they can move and squeeze together.

The boundary or contact surface between the two geographic areas is where the earthquake occurs. Pacific Ring of Fire, where the Pacific sea shell submerged beneath the South American and North American continental shells toward the East Coast; underneath the Asian continental shell to the west bank is where many seismic activities and volcanoes are recorded.

The types of earthquake patterns caused by the two blocks of blocks moving side by side in opposite directions, can be seen as the San Andreas system model Fault System (California, USA) because the North Pacific array slips across the North American array, or in Vietnam territory with systems of Ailao Shan - Song Hong faul (Indochina and South China array) and Mea Ping- Wang Chao fault (located in Indochina array) Figure 1).

Figure 1 : Loma Prieta earthquake by sliding between Pacific and North America arrays along the San Andreas ridge, the same pattern as the earthquake mechanism in Vietnam

Types of earthquakes with a shallow center from 60 km back are the type that causes damage, the types are deep down, partly because the structure of the soil here is partly unstable under the high temperature in the ground, the part because it takes a long distance to propagate to the ground, so it does not cause much damage as the group runs out.

In principle, the reasoning of the terrain is relatively unchanged, the relative movement of the two adjacent arrays will also be fixed for a geological time, so the process of storing energy on the contact surface two areas, the critical point, the sudden burst of earthquakes and earthquakes, followed by a new cycle that continues so must be periodic.

Therefore, in addition to different methods to find out how to predict the occurrence of an earthquake, Paleoseismology is an important industry for seismic research. Accordingly, studies of geologic sections selected for cross-sectional systems will provide data on the number of occurrences as well as the magnitude of the seismic sites in the survey. This information will help establish a statistical model and probability of seismic occurrence in a specific area.

In the field of geomorphology, about 65 million years ago the Indian block moved up from the southern hemisphere and touched the Eurasian continent (Eurasia), resulting in the Hymalayan paint phenomenon, establishing the Himalayas. The intense paint forces here flourished on both sides, and on the east they tore apart the Indochina block and pushed these ripped parts to the southeast.

At least 3 major cracks are recorded over time as India moves northward after hitting Eurasia. Mea Ping-Wang Chao is located south, appearing first and supposedly shut down about 15 million years before India passed by and continued moving north . The Ailao Shan - Red River begins at 15 million years and stops working about 5 million years when India moves deeper. Currently, the Altyn - Tag is considered as the current result of this motion, operating and creating seismic loads on Chinese territory.

In recent times, the occurrence of earthquakes on Indochina and especially in Vietnam has become more frequent. In the south, earthquakes appear to have a southern coastal record, especially in the Gulf of Thailand (1982) and in the Great Lake, Cambodia (1980). These epicenter locations coincided with the location of Wang Chao, thus signaling that the system, after a period of ten million years of rest, has now reactivated.

This operation is hard to explain because of the Himalayan motion that can only be explained by a new tectonic activity in the undiscovered region, or simply temporary movements that indirectly affect motion strong creation of Sumatra region today. In the north, it is clear that the earthquake occurred here due to the movement of the system of Ailao Shan - Song Hong and the Dien Bien Phu sub-system. This system, even though supposedly shut down for 5 million years now, but the geological time is too short, creating Himalayan paint can still affect these systems.

Studies by Professor Allen, University of Caltech, Passadena, Calif. (Red River and Associated Faults, Yunnan Province, China; 1984) on the northern region of the ramparts Ailao Shan - Red River, Yunnan territory showed that this massive system is still active . The author warns that the southern region of this massive system (Vietnam), which does not currently have many seismic activities, may indicate a seismic gap. Seismic gap is a part of an active system that does not show seismic activities and follow other parts of the system with seismic activity.

This is the part of the rock, where the reasoning of the two-sided rocky soil has a high resistance to displacement, which is not easily separated and created seismic. But it is this, this is where the concentrated energy is much higher than the other parts, to reach a critical boundary they will scatter with a tremendous energy and will form an extreme earthquake. great. The author warns that the massacre of Ailao Shan - Red River in Vietnamese territory may be a seismic gap, they are hibernating for a chance to wake up vigorously (Figure 2).

Figure 2 : Earthquake center recorded the northern part of the Red River (Red River), from 780 to 1976

The earthquake that struck the Lao-Myanmar border has caused vibrations on buildings in Hanoi and panicked residents here. The information in Thanh Nien, VN Express (May 18, 2007) by the authorities has reassured the people that at this level there is not much harmful impact and the collapse and the construction of The building has been prepared to resist earthquakes. But public opinion also has some other pessimistic news that Hanoi is allocated in the quake zone 8; earthquake cycle about 1,000 years; in the 12th century, a level 8 earthquake broke the stone pillar of Bao Thien pagoda .

Is this information too subjective? Although the seismograph was invented since 1880 (Chinese people invented seismic recording devices since 132), but the system recognizes Ritcher scale only invented and applied since 1935. Geomagnetic intensity The earthquake of the earthquakes before this time, was not accurately recorded but was estimated based on the similarity of the level of devastation recorded in the literature between past earthquakes and data. New facts of the current earthquakes.

Figure 3 : San Francisco Earthquake 1906, level 7.6 - 8.0

The seismic devastation of San Francisco in 1906, is believed to have level 8.1 (figure 3), but after the earthquake Loma Prieta, Calif., 1989, by digging large holes across crevices of old houses seismic compares the level of movement of the lower strata of these two earthquakes, and some other surveying methods, they suggested that the San Francisco 1906 earthquake could be only 7.6 to 8.0. .

Currently there are no similar studies on earthquakes that occur on the Red River fault area of ​​Vietnam territory, to bring to the conclusion that there have been earthquakes of level 8.0 in the past published in the country or World seismic and seismic researchers in the world. If you can look at the image of the devastating city of San Francisco due to the earthquake of 1906 (level 8.1 or smaller) or even the Cypress Freeway (Oakland) system that is squashed by Loma Peta 1989 (level 7.1), we It is difficult to accept in the 12th century a level 8.0 earthquake happened, causing a double break of the Bao Thien pagoda without causing damage to the temple and residential houses in the area but not recorded in the history books.

Vietnam is located in an area with an earthquake hazard, prevention programs, preparation of an earthquake - medical facilities for medicine, food storage, shelter facilities, water and electricity systems, systems Fire protection . for a number of millions of residents in disaster conditions occur. Training of specialists or combining or hiring experienced agencies to do Paleoseismology to result in probabilities, statistics on the likelihood of occurrence and seismic intensity in Vietnam region, to get a convincing and unified result. Educating the public about the earthquake and the appropriate response when an earthquake occurs. That is probably the problem that should be much concerned. Besides, a publication of seismic capability of level 8.0 in Vietnam leads to the demand for construction companies, domestic and foreign investors to spend more money to build and design vehicles. or earthquake prevention techniques, this must certainly bring about a lot of controversy.

Dr. Nguyen Anh Tuan - San Jose University, USA