The study on coseismic step-like changes of water-level is of theoretical and practical significance to the mitigation of secondary hazards, identification of earthquake precursors, tracking of the subsequent shocks, and the research of crustal activity (Nur and Booker, 1972;WANG et al, 1988). A lot of researches have been done by previous geoscientists. Among them, ZHANG et al (1994) inverted stress variation in the aquifers through the analysis of coseismic step-like changes of well water level. LI (1995), WANG (2000), and FU et al (2002) studied the relationship between coseismic step-like changes of water level and future seismic activity. HUANG et al (2000) investigated the water-level changes in many wells after the occurrence of one great earthquake. However, the analysis of the quantitative relation between the coseismic step-like changes of water level and earthquakes in China has not been reported so far. This paper describes the coseismic step-like changes of water level in the Dazhai well, Simao city, Yunnan Province, and tries to discuss the possible mechanism of these changes. Basic conditions of the well and principal characters of water level changesThe Dazhai observation well is located in the middle part of the Yixiangba rift basin, about 11 km in the southeast of Simao city. The rift basin is situated in the southwest part of the Jingmenkou-Shigaoqing segment of the Pu'er fault (Figure 1). The well is 112.27 m deep, installed with 150 mm diameter casing from the earth surface to 26.69 m depth. The section for water level measurement ranges from 26.69 m to 112.27 m. The diameter of water-carrying section is 108 mm. The buried depth of the top of aquifer is 7.51 m below earth surface. The well was drilled into confined aquifer in Cretaceous sandstone, with a rate of discharge of 0.3-0.6 L/s (artesian well).The hydrochemistry of the water is characterized by HCO 3 ~Ca2+-The well has been continuously monitored since January 1, 1984.Water level in the Dazhai well has been measured continuously by using mechanical float gauges, and a strip-chart analog recorder is used to record water level data. In the second half of 2001, a digital groundwater-level gauge with data-sampling interval of 1 rain has been installed. The groundwater level in the Dazhai well is primarily supplied by rainfall, and there is no withdrawal well in the vicinity. The stable observation environment, there-*
The temporal and spatial variations of surface latent heat flux (SLHF) before and after the Mw9.0 earthquake that occurred on the west coast of Sumatra, Indonesia on 26 December 2004 are summarized. It is found that before the earthquake significant SLHF anomalies occurred at the epicentral area and its vicinity. The largest SLHF anomaly occurred on the subduction zone in the middle part of Burma micro-plate, where the middle part of the rupture zone is located and the aftershocks are concentrated. The developments of the anomaly involved growing of the anomaly from small to large and spreading of the anomaly from disordered to concentrated. The anomaly began to occur on the east extensional boundary of the Burma micro-plate and its adjacent oceanic basin, and then propagated to the west compressive boundary, where the subduction zone exists. Finally, the anomaly disappeared after the main shock. The seismic source is considered to be a dissipation system. The increase of stress prior to an earthquake may enhance the exchange of energy and material between the seismic source system and the outer system, resulting in the increase of the rate of energy exchange between sea surface and atmosphere, which is believed to be the main reason of the generation of SLHF anomaly.
On the basis of digital records from Tayuan well, we study coseismic effects of water temperature caused by remote earthquakes. The records show that the water temperature changes are consistently following the process of drop-rise-recovery regardless of focal mechanism or epicentral directions. The step amplitude of water temperature increases with the increase of earthquake magnitude, and decreases with the decrease of epicentral distances. They have rather well correlation. Water temperature rising after earthquake is influenced by water level variations. Finally, the mechanisms of coseismic effects of water temperature have been discussed. Preliminary study shows that accelerated convection and mixing of different temperature water in virtue of seismic wave are the main causes of water temperature drops. Seismic wave accelerates water convection, which causes warm water to move up from deeper part of the well and cold water to go down from the upper part. Temperature probe will detect water temperature drops at early stage. After the occurrence of earthquake, as the fluctuation of water level gradually quiets down, water temperature near the probe begins to rise.
The thermal diffusivity is the key parameter that controls near-surface temperature where periodic temperature variation is progressively attenuated and delayed with depth. This article presents the results of apparent thermal diffusivity using temperatures recorded by a bedrock temperature measurement network in the fault zones of western Sichuan. High sensitivity temperature sensors (10 −4 K) were installed at a maximum depth reaching 30 m. The apparent thermal diffusivities were deduced from both amplitude damping and phase shifting of annual temperature variations between two different depths. Under pure conduction, the thermal diffusivity determined through the phase method (α Φ ) should be equivalent to that determined through the amplitude method (α A ), whereas effects of the upward (downward) water flow are evidently reflected in the amplitude decay to make α Φ larger (lesser) than α A . The discrepancy between α Φ and α A can thus be a tracer of water movement or convective heat transfer. The calculated α Φ of the measurement stations varies from 1.22 × 10 −6 to 3.00 × 10 −6 m 2 /s, and the estimated α A ranges from 0.93 × 10 −6 to 2.41 × 10 −6 m 2 /s. Two regimes of heat transfer underground were suggested from the results. Conductive heat transport prevails over the nonconductive processes at five stations, which is characterized by α Φ coincident with α A for the same depth pair. On the contrary, the values of α Φ differ from α A at six stations in the intersection area of the Y-shaped fault system, implying that convective heat transfer also plays a comparably important role.This finding is consistent with the hot springs distribution of the area. The results also indicate that water moves upward with an average Darcy velocity of approximately −1 × 10 −7 m/s in this region. Our research provides new evidence for the hydrothermal activity in the fault zones at the eastern margin of the Tibetan Plateau.
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