Coseismic Groundwater Drawdown Along Crustal Ruptures During the 2016 M_w 7.0 Kumamoto Earthquake

Abstract

Groundwater‐level changes after earthquakes provide insight into changes in hydrogeological properties such as permeability and pore pressure. Quantifying such changes, both their location and magnitude, is usually hindered by limited data. Using extensive high‐resolution water‐level monitoring records, we provide direct evidence of significant groundwater drawdown (4.74‐m maximum) over a 160‐km2 area along crustal ruptures after the Mw 7.0, 2016, Kumamoto earthquake. Approximately 106 m3 of water disappeared within 35 min after the main shock. The loss of water was not caused by static‐strain driven pore‐pressure decrease nor by releasing of water through structural pathways, but most likely by water transfer downwards through open cracks. Such changes may impact the security of water resources, the safety of underground waste repositories, and contaminant transport in seismically active areas.

Earthquake-Induced Spring Discharge Modifications: The Pescara di Arquata Spring Reaction to the August–October 2016 Central Italy Earthquakes

“…As reported by Mohr et al [12], discharge increases after earthquakes, observed mainly on stream gauges, can be explained by three mechanisms: (i) changes in static strain determining aquifer geometry modifications, pore pressure changes and consequent variations of hydraulic gradient i [3]; (ii) dynamic strain effects such as consolidation and shaking of water out of the unsaturated zone [5][6][7][8]14]; (iii) increased permeability due to dynamic strain [4,9,11,12,[15][16][17][18].…”

Hydrological changes after the 2016 Kumamoto earthquake, Japan

“…7). Hosono et al (2019) also reported both of co-seismic rises and drops in groundwater level. However, large seasonal changes, which were probably induced mainly by precipitation, were recognized at e:SOY, f:SOI, g:YSM, h:SMR, and k:DMZ.…”

“…However, large seasonal changes, which were probably induced mainly by precipitation, were recognized at e:SOY, f:SOI, g:YSM, h:SMR, and k:DMZ. Our sampling interval was much longer than that of Hosono et al (2019). Therefore, the postseismic flow rate changes in Fig.…”

“…Co-seismic volumetric effects (Montgomery et al 2003) and liquefaction (e.g., Manga 2001) also cannot explain the delayed postseismic streamflow increase in this region. Hosono et al (2019) reported both of co-seismic drops and rises in stream water level. Similar changes are also recognized in Fig.…”

“…The 2016 Kumamoto Earthquake, which occurred mainly in Kumamoto Prefecture, Japan, in April 2016 (Hirata 2016;Hashimoto et al 2017), caused severe damage in and around Kumamoto Prefecture. It also caused many changes in stream water and groundwater (Sato et al 2017;Ichiyanagi and Ando 2017;Hosono et al 2019). The 2016 Kumamoto earthquake had two main events: Japan Meteorological Agency (JMA) magnitude (Mj) 6.5 foreshock at 21:26 Japan Standard Time on April 14, 2016, and the main shock of Mj 7.3 at 01:26 on April 16, 2016.…”