**Updated webpage: ** http://srworks.jigsy.com/

(Last updated on 31st Dec. 2020.)

__O V E R V I E W__

I am interested in mathematical modeling of various physical processes; in particular, modeling related to earthquake physics. My research interests revolve around:

- Application of fracture mechanics to understand many ways of sliding along geological faults.
- Nonlinear dynamics of frictional sliding.
- Numerical methods for and approximate solutions of nonlinear partial differential equations.

__R E S E A R C H __

**When heterogeneities promote disordered slip**

Here, I explore the scenarios that can provoke disordered slip evolutions in elasto-frictional interfaces. I find that faults that include rate-strengthening regions can lack attractive blow-up solutions. In such scenarios, a rate-weakening fault that includes appropriate rate-strengthening regions can delay the development of slip instabilities. Owed to the non-existence of attractive blow-up solutions, the developing slip velocity fails to converge to a specific distribution at a single location. The near-chaotic transient dynamics may give rise to tremor-like activities.-
**Many ways of interfacial sliding: creep propagation on faults and its transition to instability**(with Dmitry I. Garagash, Dalhousie Univ.)

We investigate aseismic creep on model faults. In particular, its propagation to large distances along the fault. This study considers a sliding rate and state dependence of the fault’s frictional strength, with steady-state rate-weakening interfacial properties. The surrounding medium deforms elastically. We find that rate-weakening interfaces can exhibit a stable aseismic sliding over long distances without any stabilizing mechanisms (e.g., dilatant strengthening) or choice of frictional properties that force a large elasto-frictional lengthscale. We propose that creep penetration is due to the fault’s tendency, when driven, to reach a state of steady sliding from a locked state. Here, we define the locked state as the state of slip when the velocity is arbitrarily less than the steady-state sliding rate for a given pre-stress. **Earthquake nucleation and frictional heterogeneity**(with Robert C Viesca, Tufts Univ.)

We explored the nonlinear dynamics of earthquake nucleating frictional instabilities. In particular, we explored how frictional heterogeneities influence the development of slip instabilities. [Ray and Viesca, JGR Solid Earth 2017]**Homogenization of physical properties on faults**

Observations suggest that faults’ frictional properties are likely to be non-uniform over its extent. However, studies often consider properties to be homogeneous, or nearly so. Here, we highlight when it may not be appropriate to homogenize the frictional properties. We explore quasistatic slip evolution on faults with simple sinusoidal forms, with a characteristic wavelength of variation Λ, for variation of frictional properties. Interestingly, slip evolutions are almost identical in the limit of very small (highly heterogeneous) and large (almost homogeneous) wavelengths, compared to the nucleation length.

Therefore, in the limit of high and low wavelengths of variations, using an average estimate of an otherwise nonuniform strength parameter is appropriate. However, heterogeneity in fault frictional properties, or normal stress, is crucial to earthquake nucleation when Λ is comparable to the nucleation length or an elastofrictional scale. [Ray and Viesca, GJI, 2019].

**Creeping landslides as diffusing slip on rate-strengthening frictional faults (in the works).**

Accelerating creep of landslides could be considered an evolution of slip of a deformable thin elastic layer over a rigid base such that basal friction strengthens with slip rate. We find self-similar solutions of nonlinear slip diffusion under relevant initial conditions of external stress or slip rate. A close analogy could be drawn with Stokes’ first problem wherein a plate below a semi-infinite region of an initially static incompressible fluid is suddenly moved to result in (self-similar) diffusion of momentum. Likewise, we find relevant length scale and nonlinear manner of diffusion of slip rate when a creeping slope is suddenly imposed with high stress or slip rate.

__T E A C H I N G__

- Fall 2016:
**Statics and dynamics**(TA) - Spring 2017:
**Strength of materials**(TA) - Fall 2017:
**Statics and dynamics**(TA)

**P U B L I C A T I O N S**

- S. Ray and Viesca R. C. (2017)
*,*Earthquake nucleation on faults with heterogeneous frictional properties, normal stress.*Journal of Geophysical Research: Solid Earth*,

DOI: 10.1002/2017JB014521. - S. Ray and Viesca R. C. (2019), Homogenization of fault frictional properties.
*Geophysical Journal International*, DOI: https://doi.org/10.1093/gji/ggz327. - S. Ray (2019), Frictional heterogeneities can promote disordered slip evolution on faults. EarthArXiv. September 3. doi:10.31223/osf.io/dcszm.
- Creeping landslides as diffusing slip on rate-strengthening frictional faults (in the works).

**C O N F E R E N C E S & M E E T I N G S**

- American Geophysical Union, December ’ 20.

Aseismic creep in steady-state rate-weakening interfaces - European Geophysical Union, Share Geoscience Online, May ’ 20.

How fault creep makes its way! - Southern California Earthquake Center, SEAS Workshop, Jan.’20.

Slip complexity on faults with heterogeneous friction (online talk) - Stanford Earth, Department seminar, March 2019,

Nonlinear instability and diffusion of fault slip rate. - UMass Amherst, Nonlinear Waves Seminar, 2019,

Aseismic and seismic slip on geological faults - American Geophysical Union, 2018, Oral presentation, (Talk)

Slip instability and aseismic slip under multiple length scales of frictional heterogeneity. - Applied Math Seminar, Tufts University, 2018, Oral presentation,

Earthquake nucleation on faults: a finite-time instability problem. - Gordon Research Seminar/Conference, 2018, Oral/Poster,

Earthquake nucleation on faults under a multitude of length scales of frictional heterogeneity. GRS’18Talk - European Geophysical Union General Assembly, 2018,

Accelerated creep of a landslide with slip rate- and state-dependent basal friction

Lichen Wang, Sohom Ray, Pierre Dublanchet, and Robert C. Viesca - Dynamics Days, 2018, Ignite Talk and Poster,

The self-similar solution of diverging slip rate on faults with heterogeneous friction

Sohom Ray and Robert C. Viesca - Gordon Research Conference on Rock Deformation, 2016,

Preferential locations of slip-rate instabilities on faults determined by heterogeneous frictional properties.

Sohom Ray and Robert C. Viesca - Winter School, Cargese, Corsica, 2014, Oral,

Slip rate instability under heterogeneous fault friction - Southern California Earthquake Center, 2014 and 2015,

Preferential earthquake-nucleating locations on faults determined by heterogeneous direct-and evolution-effect parameters of rate-and state-dependent friction

Sohom Ray and Robert C. Viesca - American Geophysical Union, 2014 (and 2016) Oral (and Poster),

The evolution of earthquake-nucleating slip instabilities under spatially variable steady-state rate dependence of friction

Sohom Ray and Robert C. Viesca

__E D U C A T I O N __

- 2013-2019: Research/Teaching Assistant at Tufts University.
- 2008-11: Masters (Geophysics) IIT Roorkee.
- 2005-08: Bachelors (Physics) Delhi University.

(Last updated on 31st Dec. 2020.)