关键词: 琼北火山区, 火山活动性, 火山监测, 测震台网, 灾害预测

Abstract:

Volcanic eruption is a manifestation of crustal movement. The upper mantle inside the earth is filled with hot magma. Under great pressure, the magma will break out of the earth’s crust from the weak place along the volcanic channel and the volcanic throat. Volcanic eruption is the most intense display of the earth’s internal heat energy on the surface. Some activity characteristics and signals will be generated before volcanic eruption. Some countries have successfully predicted volcanic eruptions, and avoided a large number of casualties and economic losses.
Volcano monitoring is the basis for accurate volcano prediction and an effective method to reduce volcanic disasters. Volcano monitoring is to monitor the activity state of underground magma through various observation methods, and to capture the precursors of volcanic eruption.
The northern Hainan Island(also called Qiongbei)is one of the areas with frequent volcanic activity since the Quaternary in China. A total of 10 phases and 59 eruptions have occurred in Qiongbei area, forming more than 100 volcanoes of different sizes and shapes. Lavas with an area of about 4000km² are distributed in seven cities and counties of Haikou, Wenchang, Qionghai, Ding’an, Chengmai, Lingao and Danzhou, and Yangpu Economic Development Zone. More than 30 volcanoes with different sizes in the Shishan and Yongxing areas of the Quaternary volcanic area are arranged in a north-west direction, forming a typical central volcanic group, and the distribution of this volcanic group is controlled by the Changliu-Xiangou fault zone. The volcanic activity of the Ma’anling-Leihuling volcanic group(the largest)continued until the Holocene. This volcano is only 15km away from Haikou City, and is a typical urban volcano with potential eruption risk. Once it erupts, it will inevitably cause widespread public concern.
In order to acquaint us with the activity of Qiongbei volcano and prevent sudden volcanic disasters, a volcano monitoring network was set up in 2007 by the Hainan Earthquake Agency, which has been running well and has accumulated a large amount of observation data. We collected and sorted out the seismic, deformation, fluid and geomagnetic observation data in the Qiongbei volcanic area in the past 23 years(including the regional seismic network data before the establishment of the volcano monitoring stations), and used various methods to analyze the data. The relationship between regional volcanism and tectonics is obtained, the activity background of Qiongbei volcano is known, and the future development direction of the volcano monitoring network is proposed. In this article, we summarized and reviewed the Qiongbei volcano systematically. The results can provide a scientific basis for the planning and construction and disaster prediction of the Qiongbei volcanic area, and offer technical support for the development of follow-up volcano monitoring.
The diurnal variation of magnetic field and load/unload response ratio are used to study the electromagnetic induction of the changing magnetic field in the earth’s interior and analyze the changes in the electrical conductivity of the fluid in the deep crust of the earth. The load/unload response ratio is the function of station location and electrical conductivity of the medium underground, and thermal motion of underground masses will increase the electrical conductivity underground. The purpose of monitoring the temperature of water is to monitor the changes in geothermy at different depths, and compare and analyze the changes in water temperature at different depths and levels between the two wells. The result shows that there is no significant increase of energy in the Qiongbei volcanic area. Statistical analysis on the recorded earthquakes in the past 23 years is carried out to obtain the information about the normal background seismic activity. In recent years, the earthquake level in the volcanic area is slightly lower than the annual average(6 events), which all belong to volcanic tectonic earthquakes. The 7 GNSS observation networks can monitor the crustal deformation in Qiongbei area, and the data reflect the regional stress changes. The analyes on the results of multi-period mobile GNSS observation show that the observation stations mainly move in the southeast direction, without deflection, and the speed and direction are consistent. Each observation station has 6 baselines relative to the Ma’anling base station in the crater, and the baseline length is in a range of 72.3~42.8km. The baseline changes are mainly in a tortuous pattern, within a magnitude of ±15mm, and there are no obvious compression or extension.

The above analysis on the existing data of geomagnetism, fluids, seismometry and GNSS measurements shows that the volcanic activity of northern Hainan Province is currently in a stable state.

Key words: Qiongbei volcanic area, volcanic activity, volcano monitoring, seismic network, disaster prediction