by Ze'ev Reches, Yehuda Ben-Zion, Thomas A. Dewers, Thomas Jordan, Hiroshi Ogasawara, Gerrie van Aswegen, Susan Jane (Sue) Webb, Mark D. Zoback

The physics of earthquake processes has remained enigmatic due partly to a lack of direct and near-field observations that are essential for the validation of models and concepts. We propose to reduce significantly this limitation by conducting research in deep mines that are unique laboratories for full-scale analysis of seismogenic processes. The access to active faults at focal depths allows direct observations of ruptured fault-zones and measurements of near-field parameters before, during and after earthquakes. The mines provide a ‘missing link’ that bridges between the failure of simple and small samples in laboratory experiments, and earthquakes along complex and large faults in the crust. There is no practical way to conduct such analyses in other environment. To unravel the complexity of earthquake processes, this project is designed as integrated multidisciplinary studies of specialists from seismology, structural geology, mining and rock engineering, geophysics, rock mechanics, geochemistry and geobiology. The scientific objectives of the project are the characterization of near-field behavior of active faults before, during and after earthquakes. We intend to measure the ambient and time variation of the stress field (orientation, magnitude, heterogeneity) at the fault proximity, to characterize the fault zone structure (fault rocks and geometric complexity) and the fault zone seismic signature (guided waves and shear-wave splitting). We will determine the rupture energy balance (temperature and microstructure measurements), assess the nonlinear rheology (damage and healing) and determine rupture parameters (e.g., Dc, rupture velocity, possible existence of opening modes). The DAFSAM project includes several complementary studies of the analyses of time-dependent geochemical composition of the fault-rocks as well as the possible interaction between fault slip and microbiological activity. The practical benefits of the DAFSAM project will be evident in several fields. 1. The project will have a significant contribution to mining safety and production, particularly in remnant mining areas or anywhere that significant ore reserves are situated adjacent to large geological structures. 2. Students of disadvantaged groups of South Africa will be involved in various parts of this international project, contributing to the diversity of the professional work force in South Africa industry and academia. 3. Knowing the stress state and fault structure at depth by direct, integrated seismic, structural and mechanical analyses at depth will contribute to the oil industry. 4. Finally, the anticipated improvements in understanding of earthquake processes by the DAFSAM research will contribute to the reduction of seismic hazards on a global scale. In January 15, 2003, we submitted a proposal title “Drilling active faults in South African mines – DAFSAM” that was approved for ICDP funding in April 2003... In this addendum, we outline the developments in the DAFSAM project since April 2003, and then describe the above three components. The DAFSAM project led to the NELSAM project (Natural Earthquake Laboratory in South African Mines) that is funded by the NSF starting October 2004... initially stated in the DAFSAM proposal: Study of earthquake processes in deep mines that serve as unique laboratories for seismogenic analysis. The scientific objectives of the two projects are the characterization of nearfield behavior of active faults before, during and after earthquakes. We will determine the rupture energy balance (temperature and microstructure measurements), assess the nonlinear rheology (damage and healing) and determine rupture parameters (e.g., Dc and rupture velocity). The projects also include several complementary studies of the analyses of time-dependent geochemical composition of the fault-rocks as well as the possible interaction between fault slip and microbiological activity.

• BOREHOLE MEASUREMENTS:
• (1) Detection of fault failure and earthquake nucleation process by using a high-precision, near-field displacement meter, strainmeters, tiltmeters and broad band accelerometers;
• (2) Determine properties of fault-rocks and their changes with time and during rupture (elastic constants, in-situ stress, temperature, seismic velocity, electric field and acoustic emission). NEAR-FIELD SEISMIC STUDIES: Using dense array of broad-band instruments to detect and analyze the (1) Nucleation phases of fault instabilities;
• (2) Opening modes and motion asymmetry;
• (3) Dynamic and static stress drops and rupture velocity;
• (4) Fault zone guided waves;
• (5) Interaction among sub parallel faults. STRUCTURAL ANALYSIS Multi-scale mapping of active fault-zones in boreholes, cores and tunnels with main objectives:
• (1) Characterization the 3D geometry;
• (2) Measurements of mechanical and physical properties of fault rocks before and after earthquakes;
• (3) Analysis of in-situ evolution of fault-rocks under natural, polyaxial loading;
• (4) Analysis of slip instability, earthquake dynamics and energy balance. GEOCHEMISTRY & MICROBIOLOGY: The extreme conditions within a fault zone during an earthquake provide a unique habitat for formation of unstable minerals (or glass) and microbial life (enhanced surface area, saturated pores, and access to nutrient supplies) . INJECTION EXPERIMENTS: The injection of fluids into stressed fault zones stimulated seismicity in a wide range of cases observed around the world. We intend to inject fluids to activate loaded fault-zones when we understand the seismic behavior, structure, and mechanical properties of the target fault.

DAFSAM, Earthquakes, Faulting, ICDP-2005/14, Mining, NELSAM, Seismology, South Africa, WITWATERSRAND

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