Active Grants


Griffith, W.A. (PI), CAREER:Damage and Fracture Characteristics of Rocks Under a Broad Spectrum of Strain Rates. NSF-Geophysics/Tectonics

Brittle damage occurs in the earth’s crust via many processes ranging from very slow (fault creep) to very fast (extraterrestrial impact). The experimental response of rocks to slow loading rates has been studied to a greater extent than for fast loading rates, despite the risks posed by many natural (earthquakes, extraterrestrial impact) and anthropogenic (explosions, mine failures, projectile penetration) events. Here it is proposed to characterize the high strain rate inelastic response of rocks by following an integrated field, experimental, and theoretical study. The results will assist to improve or justify theoretical models of these rapid events and their associated brittle damage production. This project also includes a partnership with Teach for America (TFA), a national teacher corps of college graduates and professionals who commit to teach for two years and raise student achievement in public schools, to create the TFA Geocorps. The TFA Geocorps will be high-achieving secondary school teachers involved in summer research activities related to the project, who will also work alongside the Principle Investigator to develop Geophysics-based curriculum units for teaching in their own classrooms.


Griffith, W.A. (PI), The relationship between strain rate and fracture density under 2D isotropic tension, American Chemical Society – Petroleum Research Fund

Brittle fracture in fault damage zones alters permeability and storage properties of faulted reservoir rocks; therefore, our ability to predict damage zone size and fracture density based on observable fault properties is highly desirable. Field observations typically show that damage zone width and fracture density scale with fault displacement, but the mechanisms behind this scaling are still enigmatic. Recent work linking simulations of earthquake rupture with borehole observations in petroleum fields has suggested that damage zone formation may be closely related to impulsive stress fields associated with shear rupture. In the numerical simulations, brittle damage is quantified in terms of continuum plasticity, yet the constitutive behavior of brittle rock failure at rapid strain rates is poorly understood. Thus far, experimental constraints on rock failure at near tip strain rates (100 -102 s -1 ) are largely limited to compressive loading configurations, whereas coseismic damage should be substantially more pervasive in tension. To rectify this gap in understanding, I propose to implement a new experimental design to simulate rock failure under impulsive isotropic tensile stress conditions. The proposed design is a modification of traditional Split Hopkinson Pressure Bar experiments, where a uniaxial compressive pulse is converted to radial tension in a rock disk bonded between two cylinders made of more compliant, less compressible materials. I propose to explore the range of tensile stress and strain rate conditions by combining different materials in the bonded sandwich structure and comparing most-mortem fragmented rocks to predictions from theoretical fragmentation models.

Griffith, E.M. (PI), Griffith, W.A. (co-PI), GP-IMPACT: Integrating Geoscience to Engage Majors with Mathematics:iGEM2, NSF-IUSE-GEOPATHS

University of Texas at Arlington (UTA) is designated a Hispanic-serving Institution and Minority-serving Institution by the U.S. Department of Education, and its diversity index ranks 5th among national universities – a measure of where college students seeking diversity are “most likely to encounter undergraduates from racial or ethnic groups different from their own.” This proposal focuses on (1) improving the success of UTA STEM-intended majors in mathematics courses leading to calculus, courses which have D-F-Withdrawal rates of >60%, and (2) introducing these students to geoscience skills and career pathways before they decide on an intended major, ultimately increasing enrollment and diversity in the geosciences. This will be accomplished by integrating geoscience research into the curriculum of College Algebra, Precalculus, and the Mathematics Learning Resource Center (LRC) “lab” components, reaching roughly 1,000 UTA students per semester. This collaboration between Mathematics at UTA and Earth Sciences at Ohio State University will empower beginning STEM students by placing abstract mathematical concepts in a scientific context at a critical transition, which constitutes statistically a major stumbling block for many of our STEM-intended majors. This partnership is also strategic;  Earth Sciences incorporates aspects of many STEM fields, and is therefore likely to be relevant for a broad range of STEM-intended students. Our initial results from a successful pilot implementation in College Algebra in Fall 2018 are encouraging and suggest increased student engagement.

Griffith, W.A. (PI), Role of confinement in coseismic pulverization of sediments: Testing the rock record of rupture directivity on the San Jacinto Fault, Southern California Earthquake Center

Pulverized fault zone rocks (PFZR) have been linked to dynamic earthquake rupture by experimental, numerical, and natural studies, potentially preserving evidence of stresses, strain rates, and prehistoric rupture directivity. Recent observations of damage zone microstructures from the San Jacinto Fault (SJF) at Rock House Canyon, where the fault juxtaposes Cretaceous tonalites against poorly consolidated sediments of the Pleistocene Bautista Formation at the Earth’s surface, display distinct fracture characteristics on either side of the fault. Whereas tonalites display classic PFZR textures, Bautista sediments show evidence of incipient pulverization (profuse, but strongly aligned internal fracturing) at depths of 120m, but negligible internal deformation at shallower depths of ~70m.  Whearty et al. (2017) infer from these observations that pulverization in poorly consolidated sediments requires a minimum confinement pressure. We propose to define the critical confining pressure at which brittle failure initiates in Bautista sediments by collecting undeformed specimens from the field and deforming them using a new modified Split Hopkinson Pressure Bar configuration designed to study the response of sediments in a confining cell to impulsive compressive stresses. Experimental deformation products will be preserved in epoxy and compared to microstructures from the San Jacinto Fault to provide constraints on stresses, including confining stresses, and strain rates required to initiate pulverization in poorly consolidated sediments.  Furthermore, companion experiments on tonalites that initiate pulverization by rapid radial expansion will be combined with Bautista experiments to test the potential of preferred rupture directivity on the San Jacinto Fault at Rock House Canyon.