Inland Earthquakes Research Articles

Nucleation process of the 2011 northern Nagano earthquake from nearby seismic observations

The 2011 magnitude (M) 9.0 Tohoku-oki earthquake was followed by seismicity activation in inland areas throughout Japan. An outstanding case is the M6.2 Northern Nagano earthquake, central Japan, occurred 13-h after the megathrust event, approximately 400 km away from its epicenter. The physical processes relating the occurrence of megathrust earthquakes and subsequent activation of relatively large inland earthquakes are not well understood. Here we use waveform data of a dense local seismic network to reveal with an unprecedented resolution the complex mechanisms leading to the occurrence of the M6.2 earthquake. We show that previously undetected small earthquakes initiated along the Nagano earthquake source fault at relatively short times after the Tohoku-oki megathrust earthquake, and the local seismicity continued intermittently until the occurrence of the M6.2 event, being likely ‘modulated’ by the arrival of surface waves from large, remote aftershocks off-shore Tohoku. About 1-h before the Nagano earthquake, there was an acceleration of micro-seismicity migrating towards its hypocenter. Migration speeds indicate potential localized slow-slip, culminating with the occurrence of the large inland earthquake, with fluids playing a seismicity-activation role at a regional scale.

Source rupture model of the 2018 MW6.7 Iburi, Hokkaido earthquake from joint inversion of strong motion and InSAR observations

The 2018 MW6.7 Iburi earthquake shocked the eastern Iburi region to the west of the Hidaka Collision Zone in Hokkaido, which is a destructive inland earthquake. We resolved the kinematic rupture process of the event by combining strong motions (SM) and synthetic aperture radar (SAR) images in a joint inversion. The results reveal that the duration of the whole rupture is about 17s, yielding a total seismic moment of 1.4×1019 N·m (MW=6.7). The main slip area is located at a depth of approximately 24 km with a peak slip of ∼0.8m above the hypocenter. The comparison with the regional velocity model shows the earthquake was initiated in the upper mantle, while the majority of slips are located in the lower crust, which is an “aseismic” domain in the typical sandwich model. The location of the major slip area is consistent with a high-conductivity volume. We proposed a mechanism of low frictional property (<0.3) produced by high pore pressure to explain the abnormal high dip angle and centroid depth located in the ductile lower-crust. Aftershocks are distributed in areas where the Coulomb frictional stress increases due to co-seismic displacement with a mechanism conjugating to the mainshock.

Application of B and Li isotope systematics for detecting chemical disturbance in groundwater associated with large shallow inland earthquakes in Kumamoto, Japan

Application of B and Li isotope systematics for detecting chemical disturbance in groundwater associated with large shallow inland earthquakes in Kumamoto, Japan

首都直下地震緊急対策区域における市区町村の 地域残存リスク算定モデルの検討 ～エンタープライズ・リスク・マネジメント（ERM） フレームワークの適用可能性～

首都直下地震緊急対策区域における市区町村の 地域残存リスク算定モデルの検討 ～エンタープライズ・リスク・マネジメント（ERM） フレームワークの適用可能性～

Investigation of GIM-TEC disturbances before M\u2009\u2265\u20096.0 inland earthquakes during 2003\u20132017

With the rapid development of the Global Navigation Satellite System (GNSS) and its wide applications to atmospheric science research, the global ionosphere map (GIM) total electron content (TEC) data are extensively used as a potential tool to detect ionospheric disturbances related to seismic activity and they are frequently used to statistically study the relation between the ionosphere and earthquakes (EQs). Indeed, due to the distribution of ground based GPS receivers is very sparse or absent in large areas of ocean, the GIM-TEC data over oceans are results of interpolation between stations and extrapolation in both space and time, and therefore, they are not suitable for studying the marine EQs. In this paper, based on the GIM-TEC data, a statistical investigation of ionospheric TEC variations of 15 days before and after the 276 M ≥ 6.0 inland EQs is undertaken. After eliminating the interference of geomagnetic activities, the spatial and temporal distributions of the ionospheric TEC disturbances before and after the EQs are investigated and compared. There are no particularly distinct features in the time distribution of the ionospheric TEC disturbances before the inland EQs. However, there are some differences in the spatial distribution, and the biggest difference is precisely in the epicenter area. On the other hand, the occurrence rates of ionospheric TEC disturbances within 5 days before the EQs are overall higher than those after EQs, in addition both of them slightly increase with the earthquake magnitude. These results suggest that the anomalous variations of the GIM-TEC before the EQs might be related to the seismic activities.

Driving stress and seismotectonic implications of the 2013 Mw5.8 Awaji Island earthquake, southwestern Japan, based on earthquake focal mechanisms before and after the mainshock

A driving stress of the Mw5.8 reverse-faulting Awaji Island earthquake (2013), southwest Japan, was investigated using focal mechanism solutions of earthquakes before and after the mainshock. The seismic records from regional high-sensitivity seismic stations were used. Further, the stress tensor inversion method was applied to infer the stress fields in the source region. The results of the stress tensor inversion and the slip tendency analysis revealed that the stress field within the source region deviates from the surrounding area, in which the stress field locally contains a reverse-faulting component with ENE–WSW compression. This local fluctuation in the stress field is key to producing reverse-faulting earthquakes. The existing knowledge on regional-scale stress (tens to hundreds of km) cannot predict the occurrence of the Awaji Island earthquake, emphasizing the importance of estimating local-scale (< tens of km) stress information. It is possible that the local-scale stress heterogeneity has been formed by local tectonic movement, i.e., the formation of flexures in combination with recurring deep aseismic slips. The coseismic Coulomb stress change, induced by the disastrous 1995 Mw6.9 Kobe earthquake, increased along the fault plane of the Awaji Island earthquake; however, the postseismic stress change was negative. We concluded that the gradual stress build-up, due to the interseismic plate locking along the Nankai trough, overcame the postseismic stress reduction in a few years, pushing the Awaji Island earthquake fault over its failure threshold in 2013. The observation that the earthquake occurred in response to the interseismic plate locking has an important implication in terms of seismotectonics in southwest Japan, facilitating further research on the causal relationship between the inland earthquake activity and the Nankai trough earthquake. Furthermore, this study highlighted that the dataset before the mainshock may not have sufficient information to reflect the stress field in the source region due to the lack of earthquakes in that region. This is because the earthquake fault is generally locked prior to the mainshock. Further research is needed for estimating the stress field in the vicinity of an earthquake fault via seismicity before the mainshock alone.

Testing Ground-Motion Prediction Equations against Moderate Magnitude Earthquake Data Recorded in Korea

ABSTRACT The selection of ground-motion prediction equations (GMPEs) to perform seismic hazard assessments is challenging for stable continental regions that lack a sufficient number of recordings. In this study, we implement various ranking methods to test the efficiencies of a wide range of GMPEs against the recordings from three of the largest magnitude inland earthquakes that occurred in the Korean Peninsula, which belongs to an intraplate region with low seismicity. In this context, we select a total of 14 GMPEs developed for active shallow crustal zones (Next Generation Attenuation-West2 [NGA-West2] project), stable continental regions, and Korea. Three statistical approaches, including the classical residual, log-likelihood (LLH), and Euclidean distance-based ranking (EDR) methods, are used to evaluate the performance of the GMPEs. The residual analyses show that for the very short spectral period (T≤0.1 s), regionally developed GMPEs perform the best, whereas the NGA-West2 GMPEs outperform other equations for short (0.2≤T≤0.5 s) and medium to long periods (T≥0.75 s). The LLH approach is shown to favor a stable continental region GMPE that has the highest standard deviation. The EDR method, which can account for both aleatory uncertainties and model bias, is found to favor the NGA-West2 and Korean GMPEs. NGA-West2 GMPEs show the lowest model bias, whereas the Korean GMPEs exhibit the lowest residual bias. Five GMPEs selected based on the EDR method are recommended for a probabilistic seismic hazard analysis in Korea. For deterministic hazard assessment, using the Korean GMPEs for the very short spectral period and NGA-West2 GMPEs for short and medium to long periods is recommended. Overall, the stable continental region GMPEs are demonstrated to perform poorly when tested against the earthquakes recorded in Korea.

Acquisition of Knowledge through Television Programs about the Tokyo Inland Earthquake: Focusing on the Knowledge Gap Hypothesis

Acquisition of Knowledge through Television Programs about the Tokyo Inland Earthquake: Focusing on the Knowledge Gap Hypothesis

Late Cenozoic Igneous Activity and Crustal Structure in the NE Japan Arc: Background of Inland Earthquake Activity

Late Cenozoic Igneous Activity and Crustal Structure in the NE Japan Arc: Background of Inland Earthquake Activity

Wide-area seismicity anomalies before the 2011 Tohoku–Oki earthquake

SummaryThis study investigates various types of seismicity changes that occurred in several regions in and around the Tohoku District, prior to the 2011 M9.0 Tohoku–Oki earthquake. In particular, we focus on the seismicity anomalies that were revealed not only in inland local areas but also in a wide area for several years before the 2008 M7.2 earthquake in the inland Tohoku District. We reconsider these seismicity anomalies in nearly identical regions, which persisted in the extended period up until the M9 mega event. This suggests that the stress changes due to transient slow slips on the Pacific Plate boundary are more likely to be the cause of the wider seismicity changes than the slips beneath the inland earthquake. To confirm the significance, we use the two-stage stationary epidemic-type aftershock sequence model and explore the relationship between seismicity changes and stress rate changes due to slow slip by means of global navigation satellite system geodetic observations.

Tidal effects on intra-continental earthquake initiation in the Tibetan Plateau and its adjacent areas*

To investigate the tidal effects on intra-continental earthquake initiation in the Tibetan Plateau and its surrounding areas, we selected over 1,500 focal mechanism solutions of inland earthquakes (epicenter locates at least 100 km to the coastlines) from Global Centroid Moment Tensor (GCMT) project and analyzed the p-values of tidal normal and shear stress as well as tidal Coulomb failure stress. For Coulomb failure stress calculation, we used Coulomb 3.40 software. We find that: (1) p-values of tidal stress change suggests a high tidal correlation of earthquake imitations with tidal normal stress change; (2) when tidal normal stress reached the local maximum values of compression and when tidal shear stress were closed to the positive peaks, earthquakes generated more frequently; (3) particular seismogenic environments such as strong continental plate interactions and the existence of fluids or rheologic substance possibly raise the tidal correlations and (4) higher sensitivity of earthquake initiation to earth tide presents along with higher seismicity, suggesting the rate of rain energy accumulation somehow has a dominating effect on the tidal correlation of earthquake initiation.

Survey on fractures of ground anchors caused by inland earthquakes

Survey on fractures of ground anchors caused by inland earthquakes

Spatiotemporal Seismicity Evolution and Seismic Hazard Potentials in the Western East Sea (Sea of Japan)

The earthquakes in the western East Sea (Sea of Japan) mostly occur in the continental margin off the east coast of the Korean Peninsula. The seismic hazard potentials in and around the western Ease Sea are studied based on analyses of tectonic structures, seismicity features, earthquake source properties, Coulomb stress changes, and strong ground motions. The earthquake source mechanisms suggest that paleo-rifting structures in the western East Sea were activated by the current stress field. A low stress cumulation rate results in the occurrence of earthquakes with long recurrence intervals. The background seismicity suggests that earthquakes with magnitudes $$M_w$$ 5.0, 6.0, and 7.0 may occur within every $$\sim $$ 44, $$\sim $$ 336, and $$\sim $$ 2550 years at 95 % confidence level. The spatial distribution of earthquakes changes with time. Most earthquakes are clustered within $$\sim $$ 60 km from the coast. The seismicity analysis indicates an apparent increase of moderate-size ( $$M_w$$ 3–5) earthquakes since the 2011 $$M_w$$ 9.0 Tohoku-Oki megathrust earthquake. Static stress changes by moderate-size inland earthquakes induce offshore events. The seismicity and Coulomb stress changes suggest high seismic potentials around the western margin of the Ulleung basin. Earthquakes with magnitudes $$M_w$$ 6.0–7.0 in the western East Sea may produce peak ground accelerations of 0.2 g within the distance of $$\sim $$ 40–80 km, which includes the coastal regions.

The Advancement of Research on Inland Earthquake Generation 2014–2018

The 2011 Tohoku-Oki Earthquake (M9.0) significantly affected inland areas of Japan. The crust and mantle response to the magathrust earthquake induced changes in the mechanical conditions of the seismogenic zone. Here we present important progress in the research into the seismogenesis of inland earthquakes. Stress, strain, strength, and structures are key parameters affecting the occurrence of earthquakes. In particular, both the spatial and temporal changes in these parameters around the focal areas of the large inland earthquakes have been detected and modeled. These results have provided spatial potential evaluation in terms of future inland earthquake occurrence. However, we clearly recognize that, in order to understand and predict the inland earthquake generation process, it will inevitably be necessary to unify the research on various spatial and temporal scales, from problems related to long-term stress loading from plate-relative motion to instant fault response.

Estimation of radiated energy using the KiK-net downhole records—old method for modern data

SUMMARYWe use KiK-net (NIED) downhole records to estimate the radiated energy, ER, of 29 Japanese inland earthquakes with a magnitude range from Mw = 5.6 to 7.0. The method is based on the work of Gutenberg and Richter in which the time integral of S-wave ground-motion velocity-squared is measured as a basic metric of the radiated energy. Only stations within a distance of 100 km are used to minimize complex path and attenuation effects. Unlike the teleseismic method that uses mainly P waves, the use of S waves which carry more than 95 per cent of the radiated energy allows us to obtain robust results. We calibrate the method using synthetic seismograms to modernize and improve the Gutenberg–Richter method. We compute synthetic seismograms for a source model of each event with a given source function (i.e. known ER), the actual mechanism and the source-station geometry. Then, we compare the given ER with the computed energy metric to correct for the unknown effect of wave propagation and the mechanism. The use of downhole records minimizes the uncertainty resulting from the site response. Our results suggest that the currently available estimates of ER from teleseismic data are probably within a factor of 3, on average, of the absolute value. The scaled energy eR ( = ER/M0) is nearly constant at about 3 × 10−5 over a magnitude range from Mw = 5.6 to 7.0 with a slight increasing trend with Mw. We found no significant difference in eR between dip-slip and strike-slip events.

Clinical Features of Disaster-Associated Direct Deaths during Recent Inland Earthquakes in Japan.

Natural disasters, including earthquakes, cause disaster-associated direct deaths due to hazards and disaster-related deaths. This study was a retrospective and observational study that explored the effect of natural disasters on direct death. Although research reports on disaster-related deaths are common, there are few reports of disaster-associated direct death caused by events, such as house collapses, fires, and sediment-related factors. The amendment of the Building Standards Law in 1981 has made Japanese building standards more stringent. We sought to examine the determinants of the number of disaster-associated direct deaths during recent inland earthquakes in Japan. Following 2016 Kumamoto earthquakes (April 14, 21:26 [magnitude (M) 6.5], April 15, 0:03 [M 6.4], and April 16, 1:25 [M 7.3] and the subsequent numerous aftershocks), police necropsies confirmed 50 disaster-associated direct deaths (28 women [56%]). Thirty-four victims (68%) were elderly people 65 years of age or older, and 38 victims (76%) died as a result of a collapsed house. These percentages are consistent with those associated with recent inland earthquake disasters in Japan. The main finding was a linear correlation between the number of completely collapsed houses and the number of deaths due to house collapse during recent inland earthquakes in Japan (P = 0.02). It is suggested that the maintenance of houses may be important in reducing the number of disaster-associated direct deaths during inland earthquakes. The amendment of the Building Standards Law might reduce the number of disaster-associated direct deaths during inland earthquakes.

Could Present Bias have an Impact on View of Disaster Revitalization? : A case study of capital area residents&apos; view for Tokyo Inland Earthquakes

Could Present Bias have an Impact on View of Disaster Revitalization? : A case study of capital area residents&apos; view for Tokyo Inland Earthquakes

A Mid and Long Term Forcast and A Worst Scenario of Japanese Economy after the Anticipated Tokyo Inland Earthquake Disaster

A Mid and Long Term Forcast and A Worst Scenario of Japanese Economy after the Anticipated Tokyo Inland Earthquake Disaster

Characteristics of relocated hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its aftershocks with a three-dimensional seismic velocity structure

I relocated the hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its surrounding area, using a three-dimensional seismic structure, the double-difference relocation method, and the JMA earthquake catalog. After relocation, the focal depth of the mainshock became 35.4 km. As previous studies show, in south-central Hokkaido, the Hidaka collision zone is formed, and anomalous deep and thickened forearc crust material is subducting at depths of less than 70 km. The mainshock and its aftershocks are located at depths of approximately 10 to 40 km within the lower crust of the anomalous deep and thickened curst near the uppermost mantle material intrusions in the northwestern edge of this Hidaka collision zone. Like the two previous large events, the aftershocks of this event incline steeply eastward and appear to be distributed in the deeper extension of the Ishikari-teichi-toen fault zone. The highly inclined fault in the present study is consistent with a fault model by a geodetic analysis with InSAR. The aftershocks at depths of 10 to 20 km are located at the western edge of the high-attenuation (low-Qp) zone. These kinds of relationships between hypocenters and materials are the same as the 1970 and 1982 events in the Hidaka collision zone. The anomalous large focal depths of these large events compared with the average depth limit of inland earthquakes in Japan could be caused by the locally lower temperature in south-central Hokkaido. This event is one of the approximately M7 large inland earthquakes that occurred repeatedly at a recurrence interval of approximately 40 years and is important in the collision process in the Hidaka collision zone.

Development of A Novel Disaster Medical Simulation System for Validating the Flow of Medical Support Activities Following A Major Tokyo Inland Earthquake

Development of A Novel Disaster Medical Simulation System for Validating the Flow of Medical Support Activities Following A Major Tokyo Inland Earthquake