arXiv subjects

H. S. Bhat

Publications and source records attributed to H. S. Bhat.

10 recordsLinked to original sources

arXiv2026

3-D numerical modelling of the feedback between deformation and thermal structure during subduction initiation for the French Lesser Antilles

We used 3-D thermomechanical modelling to investigate conditions during subduction-zone initiation and early thermal development with focus on the Lesser Antilles. Our model imposes a convergence velocity of 2 cm per year and incorporates heating caused by irreversible deformation of mantle and crustal rocks, using elasticity, creep, and non-associative plastic flow laws. Our results show that deformational heating before slab development is unexpectedly strong. After several million years, buckling and heating due to irreversible deformation create distinctive patterns of topography and surface heat flow that resemble present-day observations, despite the slab and subduction interface being incompletely developed. Within the Caribbean plate, plate buckling produces a high topographic ridge underlain by a large positive thermal anomaly of approximately 200 K, centred just below the Moho. The conductive thermal boundary layer transporting this heat to the surface thins from about 100 km to 10 km beneath the topographic maximum, allowing the ridge to rise above sea level. This thermal structure suggests the potential initiation of a volcanic arc approximately 180 km from the inter-plate contact. A hot zone at 30-50 km depth has pressures consistent with those inferred from Lesser Antilles primitive magmas and represents the most plausible location for partial melting of Caribbean mantle if volatiles are present. The thick Caribbean crust, approximately 20-25 km, is also heated sufficiently for possible silicic melt generation. The inferred lithospheric thickness of 50-100 km aligns with tomography studies. Thus, subduction thermal structure is strongly influenced by several million years of initiation processes.

physics.geo-ph↗

arXiv2026

Quantifying the Role of 3D Fault Geometry Complexities on Slow and Fast Earthquakes

Traditional models of slow slip events (SSEs) oversimplify fault geometry, although imaging shows subduction faults are segmented and complex. We examine how fault interactions control slip behavior using 3-D quasi-dynamic earthquake sequence simulations of two parallel faults with uniform rate-weakening friction accelerated by hierarchical matrices. Four regimes emerge-periodic earthquakes, coexisting SSEs and earthquakes, only SSEs, and complex sequences-whereas with the same friction condition a single planar fault produces only earthquakes. We quantify interaction using the maximum Coulomb stress induced on a target fault by a spatially uniform unit stress drop on a neighboring fault. Because the stress drop is normalized, the metric depends only on geometry and is independent of friction, allowing extension to arbitrary fault systems. SSEs occur only at intermediate fault interaction strengths. At low interaction strengths, the system produces regular, periodic earthquakes. At high interaction strengths, fault interactions generate complex earthquake sequences with irregular recurrence and variable magnitudes. Simulations reproduce observed moment-duration scaling and show sensitivity to detection thresholds. These results demonstrate geometric complexity alone generates both slow and fast earthquakes through evolving traction heterogeneity.

physics.geo-ph↗

arXiv2026

Fault volume digital twin to reproduce the full slip spectrum, scaling and statistical laws

Seismological and geodetic observations of fault zones reveal diverse slip dynamics, scaling, and statistical laws. Existing mechanisms explain some but not all of these behaviors. We show that incorporating an off-fault damage zone-characterized by distributed fractures surrounding a main fault-can reproduce many key features observed in seismic and geodetic data. We model a 2D shear fault zone in which off-fault cracks follow power-law size and density distributions, and are oriented either optimally or parallel to the main fault. All fractures follow rate-and-state friction with parameters enabling slip instabilities. We do not introduce spatial heterogeneities in frictional properties. Using quasi-dynamic boundary integral simulations accelerated by hierarchical matrices, we simulate slip dynamics and analyze events produced both on and off the main fault. Despite spatially uniform frictional properties, we observe a natural continuum from slow to fast ruptures, as seen in nature. Our simulations reproduce the Omori law, inverse Omori law, Gutenberg-Richter scaling, and moment-duration scaling. We observe seismicity localizing toward the main fault before nucleation of main-fault events. During slow slip events, off-fault seismicity migrates in patterns resembling fluid diffusion fronts, despite the absence of fluids. We show that tremors, Very Low Frequency Earthquakes, Low Frequency Earthquakes, Slow Slip Events, and earthquakes can all emerge naturally within this fault volume framework, making it an ideal digital twin for testing hypotheses, performing ground-truth inversions, and probing mechanical properties inaccessible with natural observations.

physics.geo-ph↗

arXiv2023

Friction Laws and Numerical Modeling of the Seismic Cycle

Earthquakes rank among the most destructive manifestations of the Earth's dynamics. Can they be predicted? This is often the first question students ask. To answer that right away: no, at present it is not possible to anticipate the date, site and magnitude of future seismic events. However, there does exist a general framework to describe observations related to earthquakes and understand the processes that lead to their occurrence: the seismic cycle. This chapter introduces the reader to the friction laws from a historical to state of the art perspective. It then deals with mechanical modelling of the seismic cycle through simple analog models and finally presents some open questions and directions for future research.

physics.geo-ph↗

arXiv2022

Nucleation of laboratory earthquakes: quantitative analysis and scalings

Decades of seismological observations have highlighted the variability of foreshock occurrence prior to natural earthquakes, making thus difficult to track how earthquakes start. Here, we report on three stick-slip experiments performed on cylindrical samples of Indian metagabbro under upper crustal stress conditions (30-60 $MPa$). Acoustic emissions (AEs) were continuously recorded by 8 calibrated acoustic sensors during the experiments. Seismological parameters (moment magnitude, corner frequency and stress-drop) of the detected AEs ($-8.8 \leq Mw \leq -7 $) follow the scaling law between moment magnitude and corner frequency that characterizes natural earthquakes. AE activity always increases towards failure and is found to be driven by along fault slip velocity. Consistently for all three experiments, the stacked AE foreshock sequences follow an inverse power-law of the time to failure (inverse Omori), with a characteristic Omori time $c$ inversely proportional to normal stress. AEs moment magnitudes increase towards failure, as manifested by a decrease in b-value from $\sim 1$ to $\sim 0.5$ at the end of the nucleation process. During nucleation, the averaged distance of foreshocks to mainshock also continuously decreases, highlighting the fast migration of foreshocks towards the mainshock epicenter location, and stabilizing at a distance from the latter compatible with the predicted Rate-and-State nucleation size. Importantly, we also show that the nucleation characteristic timescale scales inversely with applied normal stress and the expected nucleation size. Finally, the seismic component of the nucleation phase is orders of magnitude smaller than that of its aseismic component, which suggests that, in this experimental setting at least, foreshocks are the byproducts of a process almost fully aseismic.

physics.geo-ph↗

arXiv2020

The Impact of Large Erosional Events and Transient Normal Stress Changes on the Seismicity of Faults

The long-term erosion of steep landscapes is punctuated by dramatic erosional events that can remove significant amount of sediments within a time-scale shorter than a seismic cycle. However, the role of such large erosional events on seismicity is poorly understood. We use QDYN, a quasi-dynamic numerical model of earthquake cycles to investigate the effect of a large erosional event on seismicity. The progressive evacuation of landslide sediments is modelled by a transient normal stress decrease. We show that erosional events with a shorter duration compared with the duration of a seismic cycle can significantly increase the seismicity rate, even for small stress changes. Moreover, large erosional events with a shorter period compared with the earthquake nucleation time-scale can change earthquake size distribution by triggering more small events. Those results suggest that large erosional events can significantly affect seismicity, illustrating in turn the short-term impact of surface processes on tectonics.

physics.geo-ph↗

arXiv2019

On the origin of thigh-frequency radiation in experimental earthquakes

We monitor dynamic rupture propagation during laboratory stick-slip experiments performed on saw-cut Westerly granite under upper crustal conditions (10-90 MPa). Spectral analysis of high-frequency acoustic waveforms provided evidence that energy radiation is enhanced with stress conditions and rupture velocity. Using acoustic recordings bandpass filtered to 400-800 kHz (7-14 mm wavelength) and highpass filtered above 800 kHz, we back projected high-frequency energy generated during rupture propagation. Our results show that the high-frequency radiation originates behind the rupture front during propagation and propagates at a speed close to that obtained by our rupture velocity inversion. From scaling arguments, we suggest that the origin of high-frequency radiation lies in the fast dynamic stress-drop in the breakdown zone together with off-fault co-seismic damage propagating behind the rupture tip. The application of the back-projection method at the laboratory scale provides new ways to locally investigate physical mechanisms that control high-frequency radiation.

physics.geo-ph↗

arXiv2018

Frictional heating processes and energy budget during laboratory earthquakes

During an earthquake, part of the released elastic strain energy is dissipated within the slip zone by frictional and fracturing processes, the rest being radiated away via elastic waves. Frictional heating thus plays a crucial role in the energy budget of earthquakes, but, to date, it cannot be resolved by seismological data. Here we investigate the dynamics of laboratory earthquakes by measuring frictional heat dissipated during the propagation of shear instabilities at typical seismogenic depth stress conditions. We perform, for the first time, the full energy budget of earthquake rupture and demonstrate that increasing the radiation efficiency, i.e. the ratio of energy radiated away via elastic waves compared to that dissipated locally, increases with increasing thermal - frictional - weakening. Using an in-situ carbon thermometer, we map frictional heating temperature heterogeneities - 'heat' asperities - on the fault surface. Combining our microstructural, temperature and mechanical observations, we show that an increase in fault strength corresponds to a transition from a weak fault with multiple strong asperities, but little overall radiation, to a highly radiative fault, which behaves as a single strong asperity.

physics.geo-ph↗

arXiv2004

Semidirect product reduction theory: a user's guide

Here we carry out computations that help clarify the Lagrangian and Hamiltonian structure of compressible flow. The intent is to be pedagogical and rigorous, providing concrete examples of the theory outlined in Holm, Marsden, and Ratiu [1998] and Marsden, Ratiu, and Weinstein [1984].

math-ph↗

arXiv2004

Lagrangian Averaging for Compressible Fluids

This paper extends the derivation of the Lagrangian averaged Euler (LAE-$α$) equations to the case of barotropic compressible flows. The aim of Lagrangian averaging is to regularize the compressible Euler equations by adding dispersion instead of artificial viscosity. Along the way, the derivation of the isotropic and anisotropic LAE-$α$ equations is simplified and clarified. The derivation in this paper involves averaging over a tube of trajectories $η^ε$ centered around a given Lagrangian flow $η$. With this tube framework, the Lagrangian averaged Euler (LAE-$α$) equations are derived by following a simple procedure: start with a given action, Taylor expand in terms of small-scale fluid fluctuations $ξ$, truncate, average, and then model those terms that are nonlinear functions of $ξ$. Closure of the equations is provided through the use of \emph{flow rules}, which prescribe the evolution of the fluctuations along the mean flow.

physics.flu-dyn↗