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The tidal response to the groundwater level refers to an aquifer under the influence of tidal forces, the pressure head (pore pressure) within the aquifer produces changes that drive the alternating transportation of water between well-aquifers, causing the rise and fall of the water level in the wells. Considering the driving process of force and seepage of water, the groundwater level response should only have a phase lag compared to the Earth's solid tides. However, the actual observation data show that the phase of the groundwater level tidal response exceeded that of the theoretical gravity tides, which is not in accordance with the commonly occurring mechanical process of the phenomenon. Using the theory of trans-current recharge, the seepage of aquifer water was decomposed into lateral and vertical transport, and the two kinds of 'lagging' transport processes were superimposed to obtain the final groundwater level tidal response, which may appear as an anomalous phenomenon in which the phase is over the front after superposition. Taking the Lugu Lake well as an example, before the Wenchuan earthquake, the phase of groundwater level was ahead of the theoretical solid tide, indicating the existence of a transgressive aquifer, whereas the groundwater level tidal factor declined from 0.28 mm/uGal before the earthquake to 0.23 mm/uGal after the earthquake. The phase, from 15 min ahead in pre-earthquake to 15 min lagged after the earthquake, combined with the theoretical analysis it can be seen that the Wenchuan earthquake led to develop the new fissure in the Lugu Lake well, thus permanently altering its aquifer response and changing the permeability of the aquifer. However, the subsequent earthquakes did not produce new fissures; only the seismic waves caused by the stress redistribution process were observed. This co-seismic response of the groundwater level shows a step-down phenomenon, phase analysis of the groundwater level has scientific significance for the study of well-aquifer conditions and well-borehole seismic capacity. [ABSTRACT FROM AUTHOR]

Thermal variations in surface and atmosphere observed from multiple satellites prior to strong earthquakes have been widely reported ever since seismic thermal anomalies were discovered three decades ago. These thermal changes are related to stress accumulation caused by the tectonic activities in the final stage of earthquake preparation. In the present paper, we focused on the thermal changes associated with the 2021 Madoi M 7.3 earthquake in China and analyzed the temporal and spatial evolution of the Index of Microwave Radiation Anomaly (IMRA) and the Index of Longwave Radiation Anomaly (ILRA) based on 8-year microwave brightness temperature (MWBT) and 14-year outgoing longwave radiation (OLR) data collected by satellites. We also explored their responses in different tectonic units (seismogenic fault zone and active tectonic block). Our results indicated that the enhanced IMRA was distributed along the seismogenic fault since mid-February and reappeared for a longer time and with stronger intensity in March and April 2021. The pronounced enhancement in the ILRA was observed within one month over Bayan Har tectonic and adjacent blocks. The higher ILRA over the tectonic blocks in the southern Tibet Plateau at the beginning of 2021 could be associated with the regional stress accumulation, as proven by the occurrences of two moderate earthquakes during this period. [ABSTRACT FROM AUTHOR]

Various physical, geophysical, geochemical, electrical and hydrological parameters are measured on the surface and in shallow/deep boreholes throughout mainland China to obtain early warning signals of impending earthquakes. Numerous wells are equipped with water level and temperature sensors for continuous observations of the water level and groundwater temperature. An analysis of water temperature data from boreholes equipped with water temperature sensors reveals that nearly half of the boreholes show coseismic response associated with the Wenchuan earthquake (Mw 7.9, 12 May, 2008). The coseismic response of the groundwater temperature cannot be differentiated from the groundwater flow or movement when the earthquake occurred, but there is no fixed relationship between the temperature variation and the water flow. At the same time, we observed that the rock temperature in dry wells can record the seismic events and even the pre-seismic abnormal information. The spatial distribution of the coseismic groundwater temperature response is random and irregular, which does not support the dislocation model of seismic faults at the regional or larger scale. Changes in the groundwater temperature are closely related to the borehole temperature gradient, lithology profile and geological environment of the borehole and depths of the aquifers. The mechanism of the coseismic groundwater temperature response can be explained by an enhanced permeability induced by an earthquake. The groundwater temperature increases if the temperature sensor in the borehole is located near the deep-circulating aquifer and decreases if the sensor is near the shallow-circulating aquifer when seismic waves arrive. The groundwater temperature may be slightly affected or even unchanged if the temperature sensor is far from the aquifer during the propagation of seismic waves. However, it was hard to conclude the changes of rock temperature observed in six dry wells. [ABSTRACT FROM AUTHOR]

The thermal anomalies associated with earthquakes using satellite infrared data are being studied in different parts of the world for more than three decades. The thermal anomalies have emerged as one of the potential earthquake precursor. However, often cloud cover obstructs detection of the thermal anomalies. Compared to infrared, passive microwave sensors provide information about the thermal radiations under any weather conditions. In the present study, we have carried out detailed analysis of brightness temperature data derived from the Defense Meteorological Space Program (DMSP) Special Sensor Microwave/Imager (SSM/I) to determine thermal anomalies associated with the 1997 Manyi and 2001 Kokoxili earthquakes. Brightness temperature data for 13 years period from 1996 to 2008 observed from F13 satellite were considered to avoid difference in the sensor sensitivity. Based on 9 years background data that ignoring data for the years in which strong earthquake occurred, we computed Index of Microwave Radiation Anomaly (IMRA) over the Manyi-Yushu Fault (MYF) and Kun Lun Fault (KLF) zones, Tibetan Plateau. Our results indicate that the microwave brightness temperature at 19.35 GHz has higher sensitivity to the seismic anomalies in comparison to the other higher frequency channels. The IMRA with multi-region, multi-frequency, and multi-parameter variation were analyzed to validate our results. In addition, variation of different parameters (microwave brightness temperature, near surface air temperature and carbon monoxide-CO) observed for Kokoxili earthquake shows the transfer process of thermal anomalies from the focal region to the atmosphere during the preparation and occurrence of earthquake. Passive microwave satellite data combined with other surface and atmospheric parameters provide better understanding of physical mechanism of thermal anomalies associated with earthquakes. [ABSTRACT FROM AUTHOR]

The primary goal of this paper is to discuss an integrated approach to efficiently obtaining earthquake damage information. We developed a framework to rapidly obtain earthquake damage information using post-earthquake airborne optical images. The framework is a standard process that includes data selection, preprocessing, damage factor identification, damage factor evaluation and the development of an earthquake damage information map. We can obtain damage information on severely affected regions using this framework, which will aid in planning rescue and rehabilitation efforts following disasters. We used the integrated approach to obtain damage information using the Lushan earthquake (magnitude 7.0, 20 April 2013) as a case study. The result were as follows: (1) 644 collapsed buildings and 4599 damaged buildings accounted for 13.90% and 96.24%, respectively, of the total number of buildings in the study area; (2) 334 landslides (total area of 691,674.5 m2) were detected and were found at greater probabilities at elevations of 1400–1500 m and higher slope; (3) no secondary disasters, such as barrier lakes, were detected; (4) 15 damaged sections (total of 306 m) were detected in the lifelines, and road sections that are at a high risk of damage (total of 2.4 km) were identified; and (5) key structures, including Yuxi River Dam and three bridges, were intact. Integrating the earthquake damage factor information generated a comprehensive Lushan earthquake damage information map. The integrated approach was proven to be effective using the Lushan earthquake as a case study and can be applied to assess earthquake damage to facilitate efficient rescue efforts. [ABSTRACT FROM AUTHOR]

A large number of civil structures were designed according to old seismic code that do not meet current safety standards. They may also suffer from ageing and deterioration induced by environmental factors such as corrosive agents and earthquakes. A methodology has been developed to assess the current state of existing structures using vibration-based structural health monitoring. This technique has attracted civil engineering community recently. Vibration-based, non-destructive damage identification uses changes in the dynamic characteristics of the structure to identify damage. Full or large-scale dynamic tests of structural specimens provide unique opportunities to evaluate and validate these methods under realistic conditions, i.e. with the same level of measurement noise, estimation uncertainty and modelling errors, which are observed as in situ conditions. In this paper, we have studied the behaviour of existing structures and the models casted in the lab. Experimental determination of the dynamic characteristics of the model of RCC building under different levels of damage has been used to develop correlation between damage in the models of RCC buildings with its known dynamic characteristics using artificial neural network models. [ABSTRACT FROM AUTHOR]

The Palghar region (north Maharashtra, India), located in the northwestern part of the stable continental region of India, experienced a low magnitude earthquake swarm, which was initiated in September 2018 and is continuing to date (as of October 2021). From December 2018 to December 2020, ~5000 earthquakes with magnitudes from M1.2 to M3.8 occurred in a small region of 20 × 10 km2. These earthquakes were probably triggered by fluid migration during seasonal rainfall. In this study, we have used multi-temporal Landsat satellite data of the year 2000, 2015, 2018, 2019, and 2020, extracted lineaments, and studied the changes in frequency and pattern of lineaments before and after the initiation of the swarm in the Palghar region. An increase in the lineament density and amount of rainfall are found to be associated with the increasing frequency of earthquakes. [ABSTRACT FROM AUTHOR]

Abstract: Recent research has shown evidence of strong coupling between the atmosphere and lithosphere in coastal regions, associating abnormal atmospheric phenomena to the occurrence of strong earthquakes. Surface latent heat flux (SLHF), total column water vapor (CWV), relative humidity (RH) and total ozone column (TOC), analyzed over the epicentral region of the Denali fault earthquake of November 3, 2002, exhibit anomalous behavior that could be related to the earthquake preparatory process and its occurrence. The complementary nature of the parameters provides strong support that the anomalous values were driven by lithospheric processes, rather than other atmospheric phenomena. Due to the wide availability of remote sensing observations of atmospheric parameters, the detection of anomalies can be used to mitigate the earthquake risks. [Copyright &y& Elsevier]

Abstract: Recent studies have shown land, ocean, atmosphere and ionospheric anomalies prior to earthquakes. The optical and microwave sensors onboard satellites are now capable of monitoring land, ocean, atmosphere and ionosphere which provide changes associated with natural hazards. In this paper, we have analyzed remote sensing data of the ocean coasts lying near the epicenters of recent four major earthquakes (Gujarat of January 26, 2001, Andaman of September 13, 2002, Algeria of May 21, 2002 and Bam, Iran earthquake of December 26, 2003), our detailed analysis shows increase of Chlorophyll-a (Chl-a) concentration associated with these recent earthquakes. The increase of Chl-a concentration is due to the change in sea surface temperature (SST) associated with the changes in stress regime in the epicentral region which is responsible for modifying the in situ thermal structure of the water and enhancing the upwelling of nutrient-rich water. The increase of Chl-a concentration also shows one to one relation with the increase of surface latent heat flux (SLHF) which is found to increase significantly prior to the earthquake events. Due to cloud cover, it has not been possible to quantify the effect of the chlorophyll concentrations associated with the earthquake events for each successive day during an event. However, the limited data from the adjacent oceanic regions provide strong evidence of the increase in Chl-a concentration. The monitoring of chlorophyll concentrations with higher spatial and temporal resolutions may provide early information about impending coastal earthquakes. [Copyright &y& Elsevier]

Changes in co-seismic water levels associated with the Gorkha Nepal earthquake (25 April 2015, Mw 7.8) were recorded in the Jingle well in Shanxi Province China (longitude E112.03 ° , latitude N38.35 ° , about 2769 km from epicenter). Based on the observed water levels, we clearly identified signals relating to P, S and surface waves. However, the water temperature recorded at a depth of 350 m shows no co-seismic changes. A spectrum analysis of co-seismic variations of water level shows that the oscillation frequency and amplitude of water level in the borehole are determined by the natural frequency of the borehole, which is not associated with the propagation of seismic waves. The borehole-aquifer system shows a large amplification associated with ground vibrations generated by earthquakes. Considering the local hydro-geological map and the temperature gradient of the Jingle well, a large volume “groundwater reservoir” model can be used to explain these processes. Due to seismic wave propagation, the volume of a well-confined aquifer expands and contracts forming fractures that change the water flow. In the well-confined aquifer, water levels oscillate simultaneously with high amplitude ground shaking during earthquakes. However, the water in the center of the “underground reservoir” remains relatively stationary, without any changes in the water temperature. In addition, a possible precursor wave is recorded in the water level at the Jingle well prior to the Gorkha earthquake. [ABSTRACT FROM AUTHOR]

The present paper shows analysis of water level (the distance from the land surface to the water in the well under static condition) and water temperature observed at three different levels of Chuan no. 03 well to study the changes associated with the Wenchuan earthquake of 2008 and the 2011 Tohoku-Oki earthquake. Our analysis shows co-seismic changes in water level and water temperature associated with the increase in compressive stress associated with the Wenchuan earthquake. The water level shows an increase, whereas there was drop in water temperature at the shallow depth (395 m) and enhancement of water temperature at the middle (595 m) and the bottom (765 m) layers. However, no step change in water level or temperature of Chuan no. 03 well is observed associated with the Tohoku-Oki earthquake, only seismic wave propagation-induced water level oscillation and led to co-seismic response of water temperature. The analysis of the co-seismic responses and post-earthquake adjustment processes combined with the borehole histogram and the borehole temperature gradient data clearly show co-seismic changes in water temperature that could be closely associated with the changes in the regional stress and strain state and the distribution of the aquifer and the characteristics of the aquifer. The observed temperature variation of different layers in the borehole is likely to be controlled by the flow of water in the horizontal direction. [ABSTRACT FROM AUTHOR]

Abstract: Earthquakes are very common natural hazards, and every year a few damaging events occur throughout the globe. Satellite remote sensing data are found to be useful in providing information about changes in land, ocean, atmosphere and ionosphere. Recent studies have shown that some of the parameters observed from the remote sensing data are associated with impending coastal earthquakes. An automatic system “CQuake” has been developed to carry out spatial and temporal data mining analysis in real time. CQuake performs retrospective analysis of earthquakes, and performs forecast for predefined regions of the world based on the analysis of Surface latent heat flux (SLHF) or any other geophysical parameters. Details of CQuake, and an example of the Colima earthquake of January 22, 2003, are discussed. [Copyright &y& Elsevier]