THOR Projects for 2016

Seismic hazard assessment of the Kathmandu basin via nonlinear ground motion, earthquake cycle and rupture simulations

( Asmaki and Ampuero)

On April 25, 2015, Nepal was hit by the magnitude 7.8 Gorkha earthquake. Contrary to the expected devastation for such a large magnitude event in a region with such poor construction practice, the observed structural damage, ground failure effects (e.g. landslides and liquefaction) and recorded ground motions showed only moderate shaking intensities throughout most of the near-field region. The death toll, while very high, was orders of magnitude lower than the number of casualties caused by similar magnitude earthquakes in regions with comparable infrastructure. The few isolated incidences of severe damage were generally associated with topographic amplification along ridge tops or with topography and basin edge effects at the outskirts of Kathmandu. The fact that the Gorkha earthquake was not nearly as devastating as we originally feared, raises nonetheless numerous urgent questions at the interface between earthquake engineering and basic earthquake research that this project addresses.

In-Situ Study of Induced Earthquake

(Avouac, Lapusta, and Ampuero)

We propose to explore the mechanics of induced seismicity taking advantage of new experimental data collected from an underground facility by our visiting collaborator Frederic Cappa. The experiment is unique in that it employs a novel instrument which allows monitoring simultaneously deformation and fluid pressure variations during fluid injection in a drill hole. We will use these data to test the applicability of models of fault dynamics in the context of induced seismicity which involves coupling between fluid flow and fault slip. Induced seismicity is of major societal concern as the increasing demand for clean energy generates accrued activities involving fluid injection or withdrawal (geothermal energy production; conventional and non-conventional oil and gas extraction; carbon dioxide sequestration). This project will also contribute to fundamental research, as the induced and natural earthquakes probably obey the same physics

Mass-Storage Enhancement for the Analysis of Dense Urban Seismic Networks

(Clayton, Tsai, and Ampuero)

We propose to add 300Tbytes of storage to our mass-storage system in order to hold a new seismic survey in the Los Angeles Basin that will be carried out in 2016. This storage will augment the system purchased under a THOR 2012 award that proved very valuable in support of a new type of seismology using dense seismic arrays.

Testing damage-detection algorithms from Earthquake damage scenarios simulated for three instrumented buildings

(Kohler, Clayton, and Asmaki)

This project seeks to numerically test damage detection methods on computational finite-element models of buildings currently instrumented by the strong-motion Community Seismic Network. Because the cost of the sensors is low making them easy to install at high densities over small areas, it is important to be able to interpret data recorded by those sensors in the face of continuously changing environments subjected to shaking and damage from earthquakes, natural hazards such as wind storms, and anthropogenic hazards such as explosions. Dense monitoring also allows building owners and businesses to minimize business disruption in the event of a moderate-to-large earthquake by making it possible for businesses to rapidly determine how quickly they can return to "business as usual." The rapid application of complementary damage detection tools allows for immediate assessment of damage, rapid emergency response, and rapid repair. Moreover, city-wide dense monitoring would make it possible for structural engineering responders to prioritize the target locations requiring first response on a floor-by-floor scale based on reports of shaking intensity.

Fluid-induced laboratory earthquakes along interfaces with rock gouge

(Rosakis and Lapusta)

Fluids play a key role in earthquake source processes. A large body of field observations have indicated the intimate connection between fluids and faulting both in natural events and in earthquakes induced by industrial activities, such as wastewater disposal associated with oil and gas production (Ake et al., 2005; Cappa et al., 2005; Dahm et al., 2010; Cappa and Rutqvist, 2011; Frohlich, 2012; Ellsworth, 2013; Gan and Frohlich, 2013; Keranen et al., 2014; McGarr et al., 2015). Fluids are known to trigger a range of seismic events spanning from earthquakes to slow, creeping motion (Segall et al., 2010; Wei et al, 2015). Yet, the mechanics underling these processes and the conditions that lead to different rupture behavior are not completely understood. We propose to study the role of fluids on faulting processes in a highly instrumented laboratory setup, which will be significantly enhanced to modulate fluid effects. To the best of our knowledge, this will be the first laboratory investigation to explore spontaneous frictional failure induced by fluid injection.