ダイラタンシーと間隙水の相変化を考慮したthermal pressurizationの自発的破壊伝播への影響

京都大学0048新制・課程博士博士(理学)甲第16633号理博第3745号新制||理||1542(附属図書館)29308京都大学大学院理学研究科地球惑星科学専攻(主査)准教授 久家 慶子, 教授 平原 和朗, 教授 中西 一郎学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

The effect of thermal pressurization on dynamic fault branching

International audienceWe numerically investigate the effect of thermal pressurization (TP) on fault branch behaviour during dynamic rupture propagation, a situation likely to occur during large earthquakes at subduction interfaces. We consider a 2-D mode II (in-plane) rupture in an infinite medium that propagates spontaneously along a planar main fault and encounters an intersection with a pre-existing branching fault. The fault system is subjected to uniform external stresses. We adopt the values used by Kame et al. We use the 2-D boundary integral equation method and the slip-weakening friction law with a Coulomb failure criterion, allowing the effective normal stress to vary as pore pressure changes due to TP. We reveal that TP can alter rupture propagation paths when the dip angle of the main fault is small. The rupture propagation paths depend on the branching angle when TP is not in effect on either of the faults, as described by Kame et al. However, the dynamic rupture processes are controlled more by TP than by the branching angle. When TP is in effect on the main fault only, the rupture propagates along the main fault. It propagates along the branch when TP is in effect on both faults. Finally, we considered the case where there is a free surface above the branch fault system. In this case, the rupture can propagate along both faults because of interaction between the free surface and the branch fault, in addition to TP on the main fault

3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

Abstract Using 3-D dynamic rupture simulations, we investigated the 2016 Mw7.1 Kumamoto, Japan, earthquake to elucidate why and how the rupture of the main shock propagated successfully, assuming a complicated fault geometry estimated on the basis of the distributions of the aftershocks. The Mw7.1 main shock occurred along the Futagawa and Hinagu faults. Within 28 h before the main shock, three M6-class foreshocks occurred. Their hypocenters were located along the Hinagu and Futagawa faults, and their focal mechanisms were similar to that of the main shock. Therefore, an extensive stress shadow should have been generated on the fault plane of the main shock. First, we estimated the geometry of the fault planes of the three foreshocks as well as that of the main shock based on the temporal evolution of the relocated aftershock hypocenters. We then evaluated the static stress changes on the main shock fault plane that were due to the occurrence of the three foreshocks, assuming elliptical cracks with constant stress drops on the estimated fault planes. The obtained static stress change distribution indicated that Coulomb failure stress change (ΔCFS) was positive just below the hypocenter of the main shock, while the ΔCFS in the shallow region above the hypocenter was negative. Therefore, these foreshocks could encourage the initiation of the main shock rupture and could hinder the propagation of the rupture toward the shallow region. Finally, we conducted 3-D dynamic rupture simulations of the main shock using the initial stress distribution, which was the sum of the static stress changes caused by these foreshocks and the regional stress field. Assuming a slip-weakening law with uniform friction parameters, we computed 3-D dynamic rupture by varying the friction parameters and the values of the principal stresses. We obtained feasible parameter ranges that could reproduce the characteristic features of the main shock rupture revealed by seismic waveform analyses. We also observed that the free surface encouraged the slip evolution of the main shock

MOESM1 of 3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

Additional file 1. Text S1: Dynamic rupture propagation in cases with unfeasible parameters. Text S2: Effects of aseismic slip triggered by foreshock 1. Figure S1: Dynamic rupture propagation in the case with the free surface when is 100 MPa, is 50 MPa (case A), is 0.35 m, and is 1.2. Figure S2: Dynamic rupture propagation in the case with the free surface when is 100 MPa, is 50 MPa (case A), is 0.1 m, and is 0.8. Figure S3: Final slip distribution in cases C, D, and G. Figure S4: Observed and synthetic near-fault ground displacements at KMMH16 (KiK-net), 93048, and 93049 (deployed by the local government of Kumamoto prefecture) stations. Figure S5: Assumed slip distribution of the aseismic slip, ΔCFS due to the aseismic slip, and ΔCFS due to the combination of the aseismic slip and the foreshocks. Figure S6: Dynamic rupture propagation in case A2 with the free surface. The stress changes due to the aseismic slip and the foreshocks were taken into account in this simulation

Rupture characteristics of the 2005 Tarapaca, northern Chile, intermediate-depth earthquake: Evidence for heterogeneous fluid distribution across the subducting oceanic plate?

We examined the rupture of the 2005 Tarapaca, northern Chile, earthquake at about 110 km depth with respect to both kinematic and dynamic characteristics by using regional and teleseismic waveforms. The earthquake has a downdip tensional focal mechanism. The subhorizontal rupture is characterized by two patches of large slip and high stress drop which are aligned nearly in the east-west direction, being perpendicular to the direction of the Chile Trench. Rupture initiated in the eastern patch and then propagated to the western patch. Between the two patches, there exists a region of nonpositive stress drop and high strength excess, which can cause subshear rupture to propagate from the eastern to the western patches but radiates little seismic waves. Seismic radiation energy from this earthquake tends to be low, which is consistent with the nonpositive stress drop and high strength excess between the two patches. While the physical mechanism of intermediate-depth earthquakes is still controversial, current leading hypotheses are associated with dehydration within subducting plates. The rupture characteristics of the Tarapaca earthquake can be related to heterogeneous fluid distribution due to the dehydration. The spatial separation and dominant stress of the two large-slip patches agree with the characteristics of the previously reported double seismic zone beneath Chile. The two patches may be the manifestation of the double seismic zone where dehydration reactions can release fluid. Using a numerical simulation of 3-D dynamic rupture, we have shown that weakening due to fluid can account for the rupture characteristics of the Tarapaca earthquake

Residents’ demographic factors by risk perception for acute radiation syndrome (ARS) might develop for general population by the FNPP accident.

<p>Note: Number refers to people within the ARS+ or ARS- group that responded with a yes. The percentages refer to the fraction of people within the ARS+ or ARS- group that responded with a yes.</p><p>Residents’ demographic factors by risk perception for acute radiation syndrome (ARS) might develop for general population by the FNPP accident.</p