Neutrino Mixing based on Mass Matrices with a 2↔32 \leftrightarrow 3 Symmetry

Under the assumption that the $2\leftrightarrow 3$ symmetry is broken only through phases, we give a systematical investigation of possible lepton mass matrix forms without referring to the explicit parameter values. The two types of the $2\leftrightarrow 3$ symmetry are investigated: one is that the left- and right-handed fields $(f_L, f_R)$ obey the symmetry, and another one is that only $f_L$ obeys the symmetry. In latter case, in spite of no $2\leftrightarrow 3$ symmetry in the Majorana mass matrix $M_R$ for $\nu_R$, the neutrino seesaw mass matrix still obey the $2\leftrightarrow 3$ symmetry. Possible phenomenologies are discussed.Comment: 12 pages, title and conclusions modifie

Dynamic Overshoot Near Trench Caused by Large Asperity Break at Depth

International audienceIn an attempt to explain the large shallow slip that occurred near the trench during the 2011 Tohoku-Oki earthquake, numerical simulations of earthquake dynamic rupture were carried out using a fault model with a subduction interface containing a bump-shaped asperity, which might result from subduction of an old submarine volcano or seamount. It was assumed that during the interseismic period, slip only occurs outside the bump area and that stress accumulates inside the bump, creating a seismogenic asperity. We roughly evaluated the amount of slip outside the bump during the interseismic period, assuming a constant long-term subduction rate. Then we could estimate the accumulated stress inside the bump. We constructed the initial stress distribution based on the stress change caused by the slip-deficit distribution. A constitutive relation was constructed based on a slip-weakening friction law and was used to compute spontaneous ruptures. The results indicate that a large slip can occur between the trench and the bump, even though a very small amount of stress is accumulated there before the rupture. This is due to an interaction between the free surface and the fault that causes slip overshoot. On the region of the fault below the bump, such overshoot cannot occur because the fault is pinned by the deeper un-slipped zone. However, on the shallower side, the edge of the fault becomes free when the rupture approaches the free surface. In this region, such a large slip can occur without releasing a large amount of stress

Synthesizing sea surface height change including seismic waves and tsunami using a dynamic rupture scenario of anticipated Nankai trough earthquakes

The development of offshore observation technology will provide researchers with tsunami records from within an earthquake focal area, but this will create new problems. Because seismic waves coexist with tsunami inside a focal area, the seismic waves could act as noise for the tsunami signal. This study shows an efficient method to calculate sea surface height change caused by an earthquake including both seismic waves and tsunami. Simulation results indicate that seismic waves overlap with tsunami; both affect the change in sea surface height although most previous tsunami studies have neglected the contribution of seismic waves. We also numerically simulated the sea-surface displacement wavefield and hypothesized results for an anticipated rupture scenario of a huge earthquake that may possibly occur in the Nankai Trough, Japan. The synthesized record could be used to evaluate the performance of a real-time tsunami prediction method. Additionally, we discussed the similarity and difference between two kinds of tsunami waveforms: the displacement of the sea surface and the pressure change at the sea bottom. Although seismic waves appeared in both waveforms, the contribution of seismic waves was lower in the displacement at the sea surface than in the pressure change at the sea bottom

地震の動的破壊のモデリング: 現実的なモデル化に必要なもの

I propose a strategy to make a numerical computation applicable to the realistic modeling of an earthquake dynamic rupture process.To do this, it is important to introduce any observables into the simulation as initial and boundary conditions.As an initial condition, distribution of total stress before the dynamic rupture, and as boundary conditions, fault constitutive relation and geometry of the fault are necessary.The initial stress distribution would be obtained by both in-situ measurements of stress and stress tensor inversions of earthquake focal mechanisms.Constitutive parameters could be obtained by near fault observations of seismic waves.Precise fault geometry can be obtained by an accurate relocation of seismicity as well as geological survey.Realistic simulations of a dynamic rupture of an earthquake can only be done by integrating the above observations

Simple Crack Models Explain Deformation Induced by Subduction Zone Megathrust Earthquakes

Following the 2010 Maule and 2011 Tohoku earthquakes, many studies have examined the relation between megathrust earthquakes and subsequent deformation. Here, we apply simple models based on mode II shear cracks, including approximated effects of the free surface to study induced deformation during coseismic and early postseismic stages. We distinguish between buried and surface ruptures represented by a full‐crack and a half‐crack model, respectively. We adopt an analogy‐based approach to interpret the half‐crack model from well‐known results of the full‐crack model, which is also validated by our numerical simulations. With transferable knowledge between the two models, we provide easy ways to understand (1) the contrasting deformation patterns in the frontal wedge of the overriding plate between buried ruptures and surface ruptures, (2) the correlation between triggered outer‐rise normal faulting and surface ruptures, and (3) the similar deformation patterns for both buried and surface ruptures toward the down‐dip end, with a preference for normal faulting in the overriding plate and for reverse faulting in the subducting plate. These model outcomes are consistent with several recent observations on aftershocks and veins in a paleoaccretionary wedge. We further investigate some important transient features during rupture propagation which show that a transition from compressional to extensional deformation in the frontal wedge of the overriding plate is possible even during a single rupture event. Our work provides alternative views for understanding various aspects of subduction zone megathrust earthquakes and raises the issue of important transient features that were typically ignored in previous studies

Preparatory acoustic emission activity of hydraulic fracture in granite with various viscous fluids revealed by deep learning technique

To investigate the influence of fluid viscosity on the fracturing process, we conducted hydraulic fracturing experiments on Kurokami-jima granite specimens with resins of various viscosities. We monitored the acoustic emission (AE) activity during fracturing and estimated the moment tensor (MT) solutions for 54 727 AE events using a deep learning technique. We observed the breakdown at 14–22 MPa of borehole pressure, which was dependent on the viscosity, as well as two preparatory phases accompanying the expansion of AE-active regions. The first expansion phase typically began at 10–30 per cent of the breakdown pressure, where AEs occurred three-dimensionally surrounding the wellbore and their active region expanded with time towards the external boundaries of the specimen. The MT solutions of these AEs corresponded to crack-opening (tensile) events in various orientations. The second expansion phase began at 90–99 per cent of the breakdown pressure. During this phase, a new planar AE distribution emerged from the borehole and expanded along the maximum compression axis, and the focal mechanisms of these AEs corresponded to the tensile events on the AE-delineating plane. We interpreted that the first phase was induced by fluid penetration into pre-existing microcracks, such as grain boundaries, and the second phase corresponded to the main fracture formation. Significant dependences on fluid viscosity were observed in the borehole pressure at the time of main fracture initiation and in the speed of the fracture propagation in the second phase. The AE activity observed in the present study was fairly complex compared to that observed in previous experiments conducted on tight shale samples. This difference indicates the importance of the interaction between the fracturing fluid and pre-existing microcracks in the fracturing process