| During the last phase of earthquake preparation,the variations of geophysical and geochemical parameters from tectonic plates and fault zones could propagate into the earth’s surface and atmosphere through the medium.These changes will be received by satellite sensors as electromagnetic waves.In the recent thirty years,the geophysical and geochemical anomalies prior to large numbers of inland earthquakes have been observed from satellites.However,coastal earthquakes have not been well considered.Three strong earthquakes,chosen based on regional geological characteristics,were selected in this study.Including the 2021 Japan M 7.1 earthquake,the 2021 Haiti M 7.2earthquake,and the 2023 Turkey M 7.8 earthquake.The multi-geosphere parameters at different vertical heights from ocean,land,and atmosphere have been analyzed in this study.The anomalies from the multi-parameters were extracted using the RST approach.By comprehensive analysis,we obtained the anomalies in the ocean,land,and atmosphere that may be related to tectonic activities.Drawing on the knowledge of oceanography and atmospheric science,as well as previous results,we proposed a conceptual model of ocean/land-atmosphere coupling associated with oceanic/coastal earthquakes.The main findings of this study are as follows:(1)Variations of multi-parameter from multiple geospheres associated with coastal earthquakes.Recently,a catastrophic earthquake(magnitude M 7.8)occurred on 6 February 2023 in Turkey.The influence of this earthquake on the adjacent ocean area(the Mediterranean)was analyzed.The obvious variations in sea temperature have been observed 5 days prior to the mainshock by processing and analyzing the spatiotemporal changes.We found that the sea surface temperature changes significantly before the main shock which shows a ‘rise-decrease’ trend.The sea potential temperature at the depth of 0-200 m shows a consistent change with the sea surface temperature.After that,a detailed regional analysis was conducted on oceanic and atmospheric parameters.The abnormal latent heat flux and sensible heat flux were found within 10 days prior to the earthquake.Significant variations were found on the day of the main shock and one day after the earthquake.The land surface temperature data was also supplemented to understand the possible mechanisms of the changes in sea surface temperature.The increased land surface temperature within 20 days before the earthquake is distributed along the active fault.The results indicate that there is a coupling relationship between geophysical and geochemical parameters within 2 weeks prior to the coastal earthquake.The possible reason is the ocean/land and atmospheric interaction caused by tectonic movements at the final phase of earthquake preparation.(2)Variations of multi-parameter from multiple geospheres associated with ocean earthquakes.Taking the Japan M 7.1 earthquake on February 13,2021 as an example,the changes in sea surface temperature around the epicenter were analyzed.The sea surface temperature shows increase and decrease in the south or the north of the epicenter,respectively.The upwelling changed the original thermal structure of the seawater one week before the main shock.The deep cold water flowing to the surface leads to a decrease in sea surface temperature.It is also accompanied by the changes in salinity and chlorophyll concentration.Additionally,the spatiotemporal variation characteristics of eight oceanic and atmospheric parameters in coastal,nearshore,and tectonic regions have been analyzed.A comparative analysis of the other three major earthquakes in Japan in 2011,2012,and 2013 has also been carried out and indicates the differential distribution pattern of abnormal signals in space and time due to different focal mechanisms.The results show the significant changes in sea temperature near the epicenter and the edge of tectonic plates prior to oceanic earthquakes.However,it should be noted that ocean circulation and weather conditions must be taken into account when analyzing earthquakes in this oceanic area.(3)Construction of a conceptual model of ocean/land-atmosphere coupling associated with oceanic/coastal earthquakes.Using the multi-parameter from six data sources,a complementary analysis of the 2021 Haiti M 7.2 has been carried out.A conceptual model of ocean/land-atmosphere coupling associated with oceanic/coastal earthquakes was proposed.The obvious changes in sea temperature were found in the epicentral region and the edge of tectonic plates.During the final stage of earthquake preparation,crustal stress builds up in the epicentral region may lead to an increase in land surface temperature.The extension of cracks and enhanced stress caused by tectonic movement are conducive to gas emissions from the Earth’s crust.The release of carbonaceous gas from the friction of faults may cause the local greenhouse effect around the epicentral region.The process of evaporation changes the latent heat flux and sensible heat flux.The sudden increase in sea surface temperature prior to the event could also be attributed to the buildup of stress in the focal regime of the earthquake and the changes in thermodynamic processes around the epicenter.The flowing seawater shows upwelling when it is close to the coastal area due to the tectonic plate subduction before the earthquake.The seawater with lower temperature and high salinity upwelling in the shallow water lead to a decline in SST and an enhancement in Chl-a concentration.Combined with the multidisciplinary knowledge of remote sensing,atmosphere science,and oceanography,a multiple geospheres coupling model of oceanic/coastal earthquakes was preliminarily constructed.The model provides a new idea for further research on oceanic/coastal seismic anomalies in other regions of the world.In the present study,the sea temperature(sea surface temperature and sea potential temperature)changes associated with oceanic and coastal earthquakes have been analyzed in detail.For the first time,we have analyzed up to 10 parameters from the ocean,land,and atmosphere to better understand the possible physical mechanism for the unusual sea temperature changes preceding the coastal earthquake.The quasisynchronous changes in different geospheres prior to earthquakes indicate the existence of a strong coupling between ocean/land and atmosphere during the final stage of earthquake preparation.However,there were some differences in the spatial and temporal distribution of abnormal signals in different cases due to the complex mechanism of earthquakes and the environment of the ocean.Although the complexity and diversity of tectonic activity from place to place,the conceptual model we proposed here provides a reference for future research on coastal/ocean earthquakes in other regions.It could be an important part of the LAIC model. |
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