EARTHQUAKE RESEARCH
Ground motion produced by earthquakes results from the combination of the source, path and site effects. A comprehensive approach to the study of these effects and its proper integration becomes essential for a realistic estimation of surface motions.
The research on these topics faces several challenges. At the source, the spatio-temporal evolution of the slip and stresses determines the way the energy is released. Clarifying how faults interact and radiate this seismic energy is a strong research concern. Along the path, the amplitude of seismic waves generally attenuates as they propagate away from the source. However, heterogeneities at regional scale produce scattering effects that need to be more profoundly understood. At local scales, seismic waves and dynamic deformations can be amplified -or attenuated- by heterogeneous superficial structures.
A unified consideration of the source, path and site effects of the elastic wave propagation becomes a necessary condition to perform, among others, appropriate implementations into the seismic hazard and early warning estimations.
The research on these topics faces several challenges. At the source, the spatio-temporal evolution of the slip and stresses determines the way the energy is released. Clarifying how faults interact and radiate this seismic energy is a strong research concern. Along the path, the amplitude of seismic waves generally attenuates as they propagate away from the source. However, heterogeneities at regional scale produce scattering effects that need to be more profoundly understood. At local scales, seismic waves and dynamic deformations can be amplified -or attenuated- by heterogeneous superficial structures.
A unified consideration of the source, path and site effects of the elastic wave propagation becomes a necessary condition to perform, among others, appropriate implementations into the seismic hazard and early warning estimations.
Main research lines
* Analysis and numerical modeling of dynamic deformations and stress changes due to tectonic loading, surface loads and seismic sources.
* 3-D Pore pressure diffusion due to surface loads and seismic sources.
* Dynamic stress transfer due to the propagation of elastic waves.
* Earthquake fault interaction and tomographic imaging of the source heterogeneities.
* Early warning systems , modeling of strong motion and seismic hazard estimates.
* 3-D Pore pressure diffusion due to surface loads and seismic sources.
* Dynamic stress transfer due to the propagation of elastic waves.
* Earthquake fault interaction and tomographic imaging of the source heterogeneities.
* Early warning systems , modeling of strong motion and seismic hazard estimates.
SOME EXAMPLES
STRESS TRANSFER AND THE TRIGGERING OF EARTHQUAKES.
Large surface water reservoirs can trigger seismicity with a wide variety of magnitudes. Different physical mechanisms that may generate earthquake triggering under saturated subsoil conditions have been proposed by several authors. These, however, are still not well understood. In this work, by the aid of a new numerical technique, we computed the evolution of the 3D subsoil stress changes and pore pressure diffusion due to the variations of the surface water load distribution and several nearby moderate-magnitude earthquakes. We studied its relation with the seismicity generated close to the Itoiz reservoir, Northern Spain. Results show a positive stress influence of the surface water loads over the main earthquakes of the series and the triggering of aftershocks due to these mainshocks. A positive pore-pressure influence due to the two largest events over most of the aftershocks was also found. These results show that at least, these two physical mechanisms were partially responsible of this seismicity.
Click image.
Click image.
SPACE-TIME CLUSTERING OF LARGE SUBDUCTION EARTHQUAKES
Most of the large destructive earthquakes (M≥6.9) that affects Mexico and western Central America mainly occur in the Mexican subduction zone. In this work we show that from the spatiotemporal scheme of epicenters of these earthquakes during the 20th century, they cluster in space and time. Here we tested the hypothesis that the coseismic stress transfer may lead to this clustering. We performed a quantitative statistical study, based on the temporal evolution of the Coulomb stress transfer, taking into account the spatial extent of ruptures. Results show that the coseismic stress transfer lead to a bimodal spatiotemporal clustering behavior, implying that once a large earthquake has taken place, the probability of occurrence of a new large event in a nearby region, increases. Click image.
Modern analysis of earthquakes depends on digital time series; however, only about 30% of the timespan of recorded seismicity is available in digital format. During the first half of the 20th century, most of the earthquake ground motions in Mexico were recorded by Wiechert mechanical instruments on smoked paper. In this work, we developed and use Tiitba, a new portable multiplatform graphical user interface (GUI) open-source software coded on python, to vectorize and correct old analogue seismograms. Using this software, we vectorized the 11/1/1928 Parral (M6.3) earthquake seismograms to obtain the constant time-interval digitized time series for each component and station of the seismogram. Then, we obtained its source focal mechanism using a genetic algorithm methodology. Also, with an auxiliary Tiitba module, we constructed a SEISAN S-file to relocate the hypocentre of this earthquake. The obtained relocation is about 125 km south of a recently recorded seismic swarm that occurred in 2013, which has a similar focal mechanism to the one that we obtained in this work.
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