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Megathrust earthquakes exhibit a ubiquitous seismic radiation style: low-frequency (LF) seismic energy is efficiently emitted from the shallowest portion of the fault, whereas high-frequency (HF) s...

Deciphering the flow below the cloud-level of Jupiter remains a critical milestone in understanding Jupiter's internal structure and dynamics. The expected high-precision Juno measurements of both the gravity field and the magnetic field might help to reach this goal. Here we propose a method that combines both fields to constrain the depth dependent flow field inside Jupiter. This method is based on a mean-field electrodynamic balance that relates the flow field to the anomalous magnetic field, and geostrophic balance that relates the flow field to the anomalous gravity field. We find that the flow field has two distinct regions of influence - an upper region in which the flow affects mostly the gravity field, and a lower region in which the flow affects mostly the magnetic field. An optimization procedure allows to reach a unified flow structure that is consistent with both the gravity and the magnetic fields.

A large earthquake (Mw 7.7) occurred on 16 April 2016 within the source region of the 1906 earthquake in the Ecuador-Colombia subduction zone. The 1906 event has been interpreted as a megathrust earthquake (Mw 8.8) that ruptured the source regions of smaller earthquakes in 1942, 1958, and 1979 in this subduction. Our seismic analysis indicated that the spatial distribution of the 2016 earthquake and its aftershocks correlated with patches of high interplate coupling strength and was similar to those of the 1942 earthquake and its aftershocks, suggesting that the 2016 and 1942 earthquakes ruptured the same asperity. Our analysis of tsunami waveforms of the 1906 event indicated Mw around 8.4 and showed that large slip occurred near the trench off the source regions of the above three historical and the 2016 earthquakes, suggesting that a depth-dependent complex rupture mode exists along this subduction zone.

Using a non-homogeneous elastic model for the south Chile subduction zone, we calculate the depth-dependent geometry of the Liquine-Ofqui Fault Zone (LOFZ), considering that faults develop where shear stress is maximum. Shear stress develops due to the oblique subduction process, depending on shear modulus which varies as a function of the amount of fluids within the overriding plate. Regions with different values of shear modulus are obtained by the geometries of isotherms calculated from a thermal model. Based on the principle that fluids move from higher to lower pressure regions, we calculate paths of fluids from the subducting slab towards the free surface. In the vicinity of the volcanic arc, the obtained fluid paths agree with the geometry of the LOFZ, suggesting that margin-parallel strike-slip faults could serve as pathways for fluids through the overriding plate in oblique subduction zones.

[1] We investigated the migration mode of deep non-volcanic tremor activity beneath Kii Peninsula, southwest Japan. Major tremor episodes are characterized by long-term migration with a velocity of about 10 km/day, propagating along the strike of the subducting plate. Similar tremor migration in Cascadia is accompanied by reverse propagation at speeds on the order of 100 km/day and much faster slip-parallel migration at speeds on the order of 1000 km/day. We systematically searched for migrating tremor with clear linearity in space and time. As a result, we found tremor migrations at speeds ranging from 1 to 60 km/hr depending on the along-dip position in the tremor zone. The observed decrease in migration speed with increasing measurement time scale suggests that migration is controlled by a diffusion process. The along-strike migration at lower speeds, including both forward and backward directions relative to the long-term migration episode, is concentrated at the updip side of the tremor zone, whereas the faster slip-parallel migration is distributed over the entire zone. The long-term migration seems to consist of and be excited by the propagation of along-strike creep at the updip part. The concentration of along-strike migrating tremor sequences at the updip side may reflect the existence of abundant fluid that accumulates at the corner of the mantle wedge. The faster slip-parallel migrations represent projections of along-strike fluctuations in slip pulse propagation controlled by striations along the plate interface.

[1] Theoretical analysis and field observations suggest that the depth‐dependent trend of permeability anisotropy is a nature of the geological media accompanying the depth‐decaying permeability. However, the effect of depth‐dependent anisotropy has not been investigated in previous studies of regional groundwater flow. A more general analytical solution of topography‐driven flow in drainage basins is derived in this study. Exponential trend of permeability with depth is assumed, and different decay rates of horizontal permeability (kx) and vertical permeability (kz) are included to account for the depth‐dependent anisotropy. It is found that the shape of the nested flow systems in a drainage basin depends on not only the depth‐dependent permeability but also the depth‐dependentanisotropyratio(kx/kz).Forstagnationpointsbetweentheflowsystems,the number of stagnation points is not influenced by the depth‐dependent permeability and anisotropy; however, an increase in kx/kz can lead to a decrease in the depth of their location. When kx is smaller than kz on the top boundary, this phenomenon is especially significant.

[1] With a new location method, we obtained a high-resolution map of non-volcanic tremor along the subducting Philippine Sea plate in southwest Japan and clarified the depth-dependent behavior of the tremor activity. A bimodal distribution of tremor along-dip is apparent in regions where short-term slow slip events (SSEs) and very-low-frequency earthquakes are frequently detected. The separation of bimodal peaks is 5 to 10 km in depth. The updip tremor activity occurs episodically, coincident with major bursts that often accompany geodetically detectable SSEs. The downdip tremor activity is, however, rather stable with frequent minor bursts. This depth-dependent tremor activity likely reflects variation of interplate slip properties, specifically weakening with increasing depth and temperature. In westernmost Shikoku, anomalous tremor activity was detected in only the updip section in late 2003. This is interpreted as being triggered by a long-term SSE in the shallower edge of the tremor zone.

[1] Previous research has indicated that for dip-slip faults embedded in a half-space, the nonvertical, asymmetric fault geometry can have a significant effect on the seismic nucleation process. Using quasi-static simulation methods and a slip-weakening friction law, we investigate the coupled effects of asymmetric fault geometry and depth-dependent frictional properties on seismic nucleation on dip-slip faults. As a first-order approximation to the depth-dependent parameters in the Earth, we assume that the normal stress tapers to a small value near the free surface, and we assume that the drop in frictional coefficient decreases with depth. We find that these depth-dependent properties have an important effect on the nucleation process of these faults: Compared to models with homogeneous frictional properties, the nucleation point moves down dip, the time to unstable slip nucleation decreases, and the amount of preseismic surface slip increases significantly. However, these effects do not dominate the effects of the asymmetric dipping geometry of these faults on the nucleation process: thrust faults nucleate farther up dip than normal faults and nucleate earlier as well. Normal faults have a larger amount of preseismic surface slip than thrust faults. The results indicate that both geometrical and frictional heterogeneity can have important effects on nucleation and that both sources of complexity must be taken into account to produce accurate models of the seismic nucleation process.

[1] A joint imaging by teleseismic converted and multiple phases is put forward to image the crustal structure beneath the INDEPTH-III passive seismic profile in the central Tibet. A depth dependent Vp/Vs ratio is adopted to map common conversion point (CCP) via a Vp/Vs scanning and stacking approach. Our new crustal image shows that the crust is divided into two sections with different Moho depth distributions and amplitudes, with the boundary nearby the Bangong-Nujiang suture (BNS). A negative P-to-S amplitude band is located in the upper-to-middle crust, indicating a low velocity zone possibly caused by partial melting beneath the negative amplitude band. The average crustal Vp/Vs ratio estimated by our joint imaging method is higher than previous study, but is consistent with a partial melting middle-to-lower crust implied by many other results.

Information on the consolidation of soil media with depth-dependent elasticity, in accord with the one-dimensional theory, is presented. The information stems from a numerical evaluation of a Fourier-Bessel series solution for the relation between the degree of consolidation and the time factor.

The vertical distribution of excess 226Ra sorbed to manganese-rich sediments from a box core taken at MANOP site H (6°34′N, 92°48′W) in the eastern equatorial Pacific can be modeled only if the rate of bioturbation decreases rapidly downward from the seafloor within the upper few centimeters of sediment. Independent bioturbation rates estimated by balancing dissolved and particulate diagenetic Mn fluxes are compatible with the values obtained from the radium model. Such results are consistent with 210Pb and 230Th measurements reported here and with MANOP lander and porewater observations that rapid organic carbon degradation in these sediments consumes oxygen within a few centimeters of the sediment-seawater interface. The modeled decrease in bioturbation (expressed as a biodiffusion coefficient) is consistent with values of more than 25 cm2/kyr at the surface falling to less than 0.4 cm2/kyr at a depth of 14 cm.