Enabling Science Interviews
Ground Motion Research - Kim Olsen discusses how he uses SDSC Compute power to conduct his ground motion research
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The macroscopic behavior of earthquake rupture depends, in part, on processes operating at the mesoscopic and microscopic scales both along rupture surfaces and in the bordering damaged rocks. Earthquake rupture propagation is strongly influenced by the balance of energy radiated as seismic waves and that associated with the breakdown in strength at the rupture tip. Creation of new fracture surfaces and frictional slip both on and off the rupture surface contribute to the breakdown energy. In spite of recent success in quantifying fracture and friction in fault zones, efforts to understand slip processes and quantify the energy budget during seismic rupture are hindered by uncertainty in the characteristics and origin of various types of damage. We are using field and laboratory data from exhumed and drilled faults, and from faults produced in the laboratory, to place constraints on the processes of dynamic weakening and the energy balance for rupture propagation. Structural observations of the Punchbowl fault, a large-displacement exhumed fault, document extreme localization of slip consistent with weakening by frictional heating. The data suggest that the creation of fracture surfaces may only account for a small fraction of the total energy budget ( < 1%), whereas the energy associated with activation of frictional slip on secondary faults away from the master fault surface is significant (3 to 10% of the total energy for a strong and weak fault model, respectively). An outstanding question is how the energy dissipated by fracture surface creation throughout the fault zone and by frictional slip off the fault surface is spatially and temporally distributed over the earthquake cycle. In particular, it is important to determine whether slip on subsidiary faults in the damage zone occurs in response to the dynamic stress concentration associated with the rupture tip, or is a result of a wear process during subsequent coseismic sliding on the main fault surface and fault creep (e.g., by sub-critical cracking) during interseismic periods. Field observations of fracture fabrics in the damage zone support the assumption that some damage is associated with dynamic rupture-tip stresses, particularly in the region near the fault surface. If a large fraction of off-fault frictional dissipation occurs during breakdown in the tip region of the earthquake rupture, then the energy available for rupture propagation and seismic radiation is diminished. Dissipation of energy by frictional slip away from the rupture surface may reduce or delay the onset of weakening processes, such as thermal fluid pressurization, at the rupture surface. Furthermore, if the damage zone of an earthquake rupture surface is characterized by significant lateral variations in fracture density, one might expect significant variations in rupture characteristics and radiation efficiency.
Judith's seminar title: "Geologic constraints on mechanisms of energy dissipation during earthquakes"; Wednesday the 24th of April 2007
ABSTRACT
We examine the potential triggering relationship between large earthquakes and methane mud volcano eruptions. Our dataset consist of a 191-year catalog (1810 to 2001) of eruptions from 77 volcanoes in Azerbaijan, Central Asia, supplemented with reports from mud volcano eruptions in Japan, Romania, Pakistan and the Andaman Islands. We compare the occurrence of historical regional earthquakes (M > 5) with the occurrence of Azerbaijan mud volcano eruptions and find the number of same-day earthquake/eruption pairs is significantly higher than expected if the eruptions and earthquakes are independent Poisson processes. The temporal correlation between earthquakes and eruptions is most pronounced for nearby earthquakes (within ~100 km) that produce seismic intensities of Mercalli 6 or greater at the location of the mud volcano. This assumed magnitude/distance relationship for triggering observed in the Azerbaijan data is consistent with documented earthquake induced mud volcano eruptions elsewhere. We also find a weak correlation that heightened numbers of mud volcano eruptions occur within 1 year after large earthquakes. The distribution of yearly eruptions roughly approximates a Poisson process, although the repose times somewhat favor a nonhomogenous failure rate, which implies that the volcanoes require some time after eruption to recharge. The volcanic triggering likely results from some aspect of the seismic wave’s passage, but the precise mechanism remains unclear.
Rob's seminar title: "Mud volcanoes and earthquakes: was the Lusi mud volcano due to drilling or an earthquake?"; Wednesday the 18th of April 2007
