Search

Fluids influence fault zone strength and the occurrence of earthquakes, slow slip events, and aseismic slip. We introduce an earthquake sequence model with fault zone fluid transport, accounting for elastic, viscous, and plastic porosity evolution, with permeability having a power‐law dependence on porosity. Fluids, sourced at a constant rate below the seismogenic zone, ascend along the fault. While the modeling is done for a vertical strike‐slip fault with 2D antiplane shear deformation, the general behavior and processes are anticipated to apply also to subduction zones. The model produces large earthquakes in the seismogenic zone, whose recurrence interval is controlled in part by compaction‐driven pressurization and weakening. The model also produces a complex sequence of slow slip events (SSEs) beneath the seismogenic zone. The SSEs are initiated by compaction‐driven pressurization and weakening and stalled by dilatant suctions. Modeled SSE sequences include long‐term events lasting from a few months to years and very rapid short‐term events lasting for only a few days; slip is ∼1–10 cm. Despite ∼1–10 MPa pore pressure changes, porosity and permeability changes are small and hence fluid flux is relatively constant except in the immediate vicinity of slip fronts. This contrasts with alternative fault valving models that feature much larger changes in permeability from the evolution of pore connectivity. Our model demonstrates the important role that compaction and dilatancy have on fluid pressure and fault slip, with possible relevance to slow slip events in subduction zones and elsewhere. Plain Language Summary: Water in the crust plays an important role in controlling the strength of fault zones and frictional sliding, which manifest as earthquakes and slow slip events that do not produce ground shaking. In this study, we perform computer modeling of earthquake sequences that are coupled to the evolution of fluid pressure and rock properties. In particular, compaction or dilation of the water‐filled pore space in rock drives changes in fluid pressure and influences the fault's frictional resistance to slip. The model quantifies the effects of compaction and dilation on both large earthquakes and slow slip events, providing specific predictions regarding slow slip event properties, pressure changes, and changes in fluid flow that might be testable with geophysical, geologic, and geochemical data. Key Points: Fluid pressure changes from pore compaction and dilatancy influence slow slip events in our modelModeled slow slip events span long‐term events lasting for months to years to rapid short‐term events for a few daysEarthquake recurrence interval is controlled in part by compaction‐driven pressurization and weakening [ABSTRACT FROM AUTHOR]

Offshore sensor networks like DONET and S‐NET, providing real‐time estimates of wave height through measurements of pressure changes along the seafloor, are revolutionizing local tsunami early warning. Data assimilation techniques, in particular, optimal interpolation (OI), provide real‐time wavefield reconstructions and forecasts. Here we explore an alternative assimilation method, the ensemble Kalman filter (EnKF), and compare it to OI. The methods are tested on a scenario tsunami in the Cascadia subduction zone, obtained from a 2‐D coupled dynamic earthquake and tsunami simulation. Data assimilation uses a 1‐D linear long‐wave model. We find that EnKF achieves more accurate and stable forecasts than OI, both at the coast and across the entire domain, especially for large station spacing. Although EnKF is more computationally expensive than OI, with development in high‐performance computing, it is a promising candidate for real‐time local tsunami early warning. Plain Language Summary: Recent years have seen more research on tsunami early warning using data from seafloor pressure sensors. Forecasts of the tsunami wave height can be computed by incorporating the pressure observations into the physical model of wave propagation. The current approach uses a simple, constant linear interpolator to blend the data with the model forecast. To improve the accuracy and stability of the forecast, we propose a more mathematically sophisticated approach that dynamically updates this interpolator, as the physical model evolves and as more data become available. This will incorporate more information into the forecast and optimize it. Using a scenario tsunami from our earthquake‐tsunami coupled simulation in the Cascadia subduction zone, we run our proposed data assimilation approach. The predicted wave heights across the ocean and at the coast are more accurate and consistent over time. More reliable forecasts can therefore be issued to coastal residents earlier in the event of a destructive tsunami. Although our method takes longer to run, with greater computing power and more efficient implementation, it is a promising candidate for real‐time tsunami early warning. Key Points: We propose an alternative tsunami wavefield assimilation method, the ensemble Kalman filterThe methods are tested on scenario tsunami in Cascadia from fully coupled dynamic earthquake and tsunami simulationEnsemble Kalman filter achieved more accurate and stable forecasts compared to optimal interpolation [ABSTRACT FROM AUTHOR]

Fault-zone fluids control effective normal stress and fault strength. While most earthquake models assume a fixed pore fluid pressure distribution, geologists have documented fault valving behavior, that is, cyclic changes in pressure and unsteady fluid migration along faults. Here we quantify fault valving through 2-D antiplane shear simulations of earthquake sequences on a strike-slip fault with rate-and-state friction, upward Darcy flow along a permeable fault zone, and permeability evolution. Fluid overpressure develops during the interseismic period, when healing/sealing reduces fault permeability, and is released after earthquakes enhance permeability. Coupling between fluid flow, permeability and pressure evolution, and slip produces fluid-driven aseismic slip near the base of the seismogenic zone and earthquake swarms within the seismogenic zone, as ascending fluids pressurize and weaken the fault. This model might explain observations of late interseismic fault unlocking, slow slip and creep transients, swarm seismicity, and rapid pressure/stress transmission in induced seismicity sequences. Coupling between fault zone fluid flow, permeability evolution, and elastic stress transfer produces fault valving and fluid-driven aseismic slip and pore pressure pulses. This model might explain late interseismic fault unlocking, slow slip, and rapid pressure transmission in induced seismicity. [ABSTRACT FROM AUTHOR]