Abstract
Hot spring discharge was linked to the 2011 Mw 6.6 Iwaki earthquake. Periodic surveys revealed that the discharge continued for more than 7 years, which is a rare and valuable long-term record of hot spring discharge triggered by an earthquake in a non-volcanic area. In terms of coseismic changes, based on a comparison of the spatial distribution of changes in the coseismic water head and calculated crustal volumetric strain using a fault model, hot spring water discharge was found to be caused by a change in the coseismic crustal volumetric strain. As for the postseismic changes, observations over 7 years revealed a gradual rise in the temperature and chloride ion concentration of the hot spring water. Such long-term hot spring discharge may be explained by the following two causes: the rise of thermal water from the deep part and the permeability changes along the hot spring channels.
Highlights
The phenomenon of hot spring water flows being renewed after an earthquake has been documented in several regions (Hosono et al 2018; Manga and Rowland 2009; Okuyama et al 2016; Wang et al 2004a)
Spatial coseismic groundwater level changes in Iwaki City To investigate the hydrological impact of the 2011 Iwaki earthquake, we surveyed the water head changes in the hot springs in the Iwaki area
We conducted a spatial and temporal survey of the changes in hot springs generated at Iwaki in relation to the 2011 Iwaki earthquake
Summary
The phenomenon of hot spring water flows being renewed after an earthquake has been documented in several regions (Hosono et al 2018; Manga and Rowland 2009; Okuyama et al 2016; Wang et al 2004a). Such long-term (i.e., more than a year) hot spring water and groundwater discharge occasionally occur in volcanic areas (Hosono et al 2018; Okuyama et al 2016) This is because volcanic fluid rises in volcanic areas, in which underground hot spring water reservoirs characterized by high pressure are likely to exist. High-pressure hot spring water reservoirs in non-volcanic areas exist within narrow boundaries, such as areas where the crust is pressured by tectonic activity due to plate or fault movement (Oki et al 1999; Roberts et al 1996) It is plausible for hot spring water and groundwater to continue to discharge for more than a year even in non-volcanic areas. Using radioactive iodine dating, they estimated that the ascent of hydrothermal fluid was 2–5 mm/year
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