scholarly journals Surface displacements of Aso volcano after the 2016 Kumamoto earthquake based on SAR interferometry: implications for dynamic triggering of earthquake–volcano interactions

2019 ◽  
Vol 218 (2) ◽  
pp. 755-761
Author(s):  
Wataru Yamada ◽  
Kazuya Ishitsuka ◽  
Toru Mogi ◽  
Mitsuru Utsugi
Keyword(s):  
Synthetic Aperture Radar ◽  
Main Shock ◽  
Synthetic Aperture ◽  
Source Depth ◽  
2016 Kumamoto Earthquake ◽  
Aso Volcano ◽  
Kumamoto Earthquake ◽  
Surface Displacements ◽  
The 2016 Kumamoto Earthquake ◽  
Aperture Radar

SUMMARY The 2016 Kumamoto earthquake involved a series of events culminating in an Mw 7.0 main shock on 2016 April 16; the main-shock fault terminated in the caldera of Aso volcano. In this study, we estimated surface displacements after the 2016 Kumamoto earthquake using synthetic aperture radar interferometry analysis of 16 Phased Array Type L-band Synthetic Aperture Radar-2 images acquired from 2016 April 18 to 2017 June 12 and compared them with four images acquired before the earthquake. Ground subsidence of about 8 cm was observed within about a 3 km radius in the northwestern part of Aso caldera. Because this displacement was not seen in data acquired before the 2016 Kumamoto earthquake, we attribute this displacement to the 2016 Kumamoto earthquake. Furthermore, to estimate the source depth of the surface displacement, we applied the Markov chain Monte Carlo method to a spherical source model and obtained a source depth of about 4.8 km. This depth and position are nearly in agreement with the top of a low-resistivity area previously inferred from magnetotelluric data; this area is thought to represent a deep hydrothermal reservoir. We concluded that this displacement is due to the migration of magma or aqueous fluids.

scholarly journals Hydrological changes after the 2016 Kumamoto earthquake, Japan

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Naoji Koizumi ◽  
Shinsuke Minote ◽  
Tatsuya Tanaka ◽  
Azumi Mori ◽  
Takumi Ajiki ◽  
...  
Keyword(s):  
Main Shock ◽  
2016 Kumamoto Earthquake ◽  
Kumamoto Earthquake ◽  
Daily Streamflow ◽  
Hydrological Changes ◽  
The 2016 Kumamoto Earthquake ◽  
Streamflow Data ◽  
Spring Flow ◽  
Water Springs ◽  
Water Holding

AbstractThe 2016 Kumamoto earthquake, whose main shock was an M7.3 event on April 16, 2016, 28 h after a foreshock of M6.5, caused severe damage in and around Kumamoto Prefecture, Japan. It also caused postseismic hydrological changes in Kumamoto Prefecture. In this study, we analyzed daily streamflow data collected by eight observation stations from 2001 to 2017 in regions that experienced strong ground motion during the 2016 Kumamoto earthquake. We also surveyed 11 water springs in the region several times after the main shock. Streamflow had no or slight change immediately after the earthquake; however, large increases were recorded at some of the eight stations following a heavy rainfall that occurred 2 months after the earthquake. A decrease in the water-holding capacity of the catchment caused by earthquake-induced landslides can explain this delayed streamflow increase. Conversely, earthquake-related changes to the spring flow rate were not so clear. Water temperature and chemical composition of spring waters were also hardly changed. Only the concentration of NO3−, which is usually considered to be supplied from the surface, changed slightly just after the earthquake. These results show that the postseismic hydrological changes were caused mainly by earthquake-induced surface phenomena and that there was little contribution from hydrothermal fluid.

The Influences of Residents’ Evacuation Patterns in the 2016 Kumamoto Earthquake on Public Risk Perceptions and Trust Toward Authorities

2017 ◽  
Vol 12 (6) ◽  
pp. 1139-1150 ◽  
Author(s):  
Shoji Ohtomo ◽  
Reo Kimura ◽  
Naoshi Hirata ◽  
◽  
◽  
...  
Keyword(s):  
Risk Perception ◽  
Risk Communication ◽  
Main Shock ◽  
Japan Meteorological Agency ◽  
Earthquake Risk ◽  
2016 Kumamoto Earthquake ◽  
The Public ◽  
Kumamoto Earthquake ◽  
The 2016 Kumamoto Earthquake ◽  
Public Risk

The 2016 Kumamoto earthquake consisted of a magnitude 6.2 foreshock that occurred on the 14th of April, and a magnitude 7.3 main shock that occurred on the 16th of April. The main shock occurring over the magnitude 6.2 foreshock was not anticipated because the foreshock was originally considered to be the main shock. After the earthquakes occurred, the Japan Meteorological Agency (JMA) discontinued its policy of announcing the probability of aftershock occurrences. The experience of the Kumamoto earthquake and the policy change concerning risk communication may affect the public risk perception of earthquakes, as well as the public trust toward authorities. In this study, we examined the reasons residents made the decision to evacuation both the foreshock and the main shock. Moreover, we investigated how residents perceived subsequent earthquake risk and they evaluate similarity and trust toward the authorities (the JMA, government, mass media, prefecture, and municipality). This study analyzed data from a mail survey implemented by the MEXT of Japan in the areas of the Kumamoto prefecture that were damaged by the earthquake. As a result, there were differences in the reasons for evacuation decisions between the foreshock and the main shock. Although residents decided to evacuate based on a fear of disaster in the foreshock, they decided to evacuate the main shock based on neighborhood communication. Moreover, the residents’ evacuation patterns influenced the earthquake risk perception. As well, the evacuation pattern influenced similarity toward the authorities and then reduced trusts toward the authorities. This study indicates that residents amplified the evaluations of the authorities after the earthquake. The influences of similarities toward the authorities became salient as a determinant of trust. This study reveals features of residents’ risk reactions to the earthquake, and discusses the importance of the similarity of the authorities for disaster risk communication.

scholarly journals Source Characteristics of the 28 September 2018 Mw 7.4 Palu, Indonesia, Earthquake Derived from the Advanced Land Observation Satellite 2 Data

2019 ◽  
Vol 11 (17) ◽  
pp. 1999 ◽  
Author(s):  
Yongzhe Wang ◽  
Wanpeng Feng ◽  
Kun Chen ◽  
Sergey Samsonov
Keyword(s):  
Synthetic Aperture Radar ◽  
Main Shock ◽  
Least Square ◽  
Synthetic Aperture ◽  
Coseismic Deformation ◽  
The South ◽  
Land Observation Satellite ◽  
Step Over ◽  
Central Sulawesi ◽  
Aperture Radar

On 28 September 2018, an Mw 7.4 earthquake, followed by a tsunami, struck central Sulawesi, Indonesia. It resulted in serious damage to central Sulawesi, especially in the Palu area. Two descending paths of the Advanced Land Observation Satellite 2 (ALOS-2) synthetic aperture radar (SAR) data were processed with interferometric synthetic aperture radar (InSAR) and pixel tracking techniques to image the coseismic deformation produced by the earthquake. The deformation measurement was used to determine the fault geometry and the coseismic distributed slip model with a constrained least square algorithm based on the homogeneous elastic half-space model. We divided the fault into four segments (named AS, BS, CS and DS, from the north to the south) in the inversion. The BS segment was almost parallel to the DS segment, the CS segment linked the BS and DS segments, and these three fault segments formed a fault step-over system. The Coulomb failure stress (CFS) change on the causative fault was also calculated. Results show that the maximum SAR line-of-sight (LOS) and horizontal deformation were −1.8 m and 3.6 m, respectively. The earthquake ruptured a 210-km-long fault with variable strike angles. The ruptured pattern of the causative fault is mainly a sinistral slip. Almost-pure normal characteristics could be identified along the fault segment across the Palu bay, which could be one of the factors resulting in the tsunami. The main slip area was concentrated at the depths of 0–20 km, and the maximum slip was 3.9 m. The estimated geodetic moment of the earthquake was 1.4 × 1020 Nm, equivalent to an earthquake of Mw 7.4. The CFS results demonstrate that the fault step-over of 5.3 km width did not terminate the rupture propagation of the main shock to the south. Two M>6 earthquakes (the 23 January 2005 and the 18 August 2012) decreased CFS along CS segment and the middle part of DS segment of the 2018 main shock. This implies that the stress release during the previous two earthquakes may have played a vital role in controlling the coseismic slip pattern of the 2018 earthquake.

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