According to the statistics from 1900 to 1983, there were 405
tsunamis in the Pacific region, among which 84 caused casualties
and significant economic losses, that is, one tsunami per year on
average. Others believe that there will be a destructive tsunami
in the region at least every 18 months.
The world tsunami-prone areas are Hawaiian Islands, Alaska Region,
Kamchatka-Kuril islands, Japan and its surrounding areas, China and
its adjacent areas, Philippine Islands, Indonesia, New Guinea region-Solomon
Islands, New Zealand-Australia and South Pacific Region, Colombia-Ecuador
North and Chile Coast, Central America and the United States, and West
Coast of Canada, and the northeastern Mediterranean coastal areas, etc.
Distribution of global earthquake-tsunami areas is basically consistent
with seismic zones. According to statistics over 1700 years, there are
about 260 recorded destructive earthquakes and tsunamis in the world,
with an average of 67 years, among them, about 80% occurred in the circum-Pacific
seismic belt, 8% occurred in the Mediterranean region, earthquakes in Japan's
islands and adjacent sea areas accounted for about 60% of the Pacific earthquake
and tsunami, therefore, Japan is the country with the most frequent earthquakes,
tsunamis and serious hazards in the world.
Overview of tsunami in China
According to historical records, only 10 earthquakes and tsunamis have
occurred in China in the past 2000 years, with an average of about 200 years.
This shows that there is little possibility of earthquake and tsunami along
the coast of China. Due to the sea area of our country is located on the
broad continental shelf with shallow water depth, mostly within 200 meters,
which is not conducive to the formation and spread of earthquake and tsunami.
Geologically, except Tancheng-Lujiang fault, which runs through the Bohai sea,
there are few large fault zones and fault belts in coastal areas, and few
island arcs and trenches in China's sea areas. Therefore, even if strong
earthquakes occur in China's seas, they generally do not cause large-scale
vertical uplift and subsidence of the seabed crust, and lack of large earthquakes
triggering tsunamis. The results of four major earthquakes in Bohai sea,
Yangjiang, Haicheng, Liaoning province and Tangshan, Hebei Province, from 1969
to 1978, which can be seen that although the earthquake magnitudes are above
6, none of them triggered an earthquake-tsunami.
What is the impact of the earthquake tsunami in the Pacific seismic belt on
China's coastal areas? Thousands of islands and reefs are distributed in the
vast coastal waters of China. From Miaodao Islands in the Bohai sea to Gounansha
Islands in the Yellow Sea, Zhoushan Islands in the East China sea, Taiwan Island
and the South China Sea Islands, these islands form an arc around the continent,
forming a sea barrier; near the coast of China, there are Kyushu, Ryukyu Islands,
and surround Philippine Islands, which constitute another natural breakwater to
withstand the violent impact of tsunami waves. Coupled with the effect of the
friction resistance of the shallow sea bottom of the broad continental shelf,
when the tsunami wave from the deep sea to the sea area of China, its energy has
been rapidly attenuated, has not become a threat. When the Chilean tsunami occurred
and the tsunami wave spread to Shanghai, only 15 to 20 cm tsunami wave height was
recorded at Wusongkou tide station; when reached Guangzhou, only weak traces of the
earthquake tsunami wave were detected at Zhapo Ocean Station. It can be concluded
that not only is the coastal areas of China not prone to earthquake and tsunami, but
also the offshore earthquake and tsunami will not pose a threat to the coastal
areas of China. Of course, it is still necessary to strengthen the research on the
occurrence mechanism of earthquake and tsunami, accurately predict and forecast
earthquake and tsunami, and it is meaningful to prevent sudden earthquake and tsunami.
Although China's offshore waters do not have the oceanic conditions of earthquake
and tsunami, nevertheless, the onshore surge of tidal water with a height of
1〜2m caused by the earthquake has occurred. If strong earthquakes of magnitude
7.5 or above occur, the Bohai Sea and the North Yellow Sea will not be affected
by earthquake and tsunami, but may cause some disasters to Taiwan and its vicinity.
It can be seen that earthquake and tsunami are still a marine disaster that cannot
be ignored in China, especially in Fujian and Taiwan regions, the potential
danger of local earthquake and tsunami disasters still exist.