The variations of elastic parameters and attenuation of rock under deformation are of great importance for a number of geophysical problems. Here, we estimate elastic parameters and their evolutions during laboratory rock deformation experiments, while developing a Monte-Carlo full-waveform fitting method. The transducer-transducer one-source one-station active seismic data of dry and water-saturated samples are obtained from Zaima and Katayama (2018, https://doi.org/10.1029/2018JB016377). The synthetic seismic data are modeled using the spectral element method. We first performed a trial-and-error estimate of the boundary conditions in order to suppress its influence on waveform matching. The synthetic seismic data are generated using equivalent homogeneous models with different combinations of elastic and anelastic parameters. We then compared the synthetics with the laboratory experimental data. Based on these comparisons, we obtain the time-lapse variations of seismic velocities and attenuation of rock samples during deformation, which are then interpreted as crack development. Our simultaneous estimation of elastic and anelastic parameters allowed us to detail the dynamics prior to the rock failure.

The NASA InSight mission to Mars successfully landed on November 26th, 2018 in Elysium Planitia. It aims to characterize the seismic activity and constrain the internal structure of Mars. We focus on the Cerberus Fossae region, a giant fracture network of ~1200 km long situated east of the InSight landing site, and where M~3 marsquakes were detected during the past two years. It is formed of five main fossae located on the southeast of the Elysium Mons volcanic rise. We perform a detailed mapping of the entire system based on high resolution satellite images and Digital Elevation Models. The refined cartography reveals a range of morphologies associated with dike activities at depth. Width and throw measurements of the fossae are linearly correlated, suggesting a possible tectonic control on the shapes of the fossae. Widths and throws decrease toward the east, indicating the long-term direction of propagation of the dike-induced graben system. They also give insights into the geometry at depth and how the possible faults and fractures are rooted in the crust. The exceptional preservation of the fossae allows us to detect up to four scales of segmentation, each formed by a similar number of 3-4 segments/subsegments. This generic distribution is comparable to continental faults and fractures on Earth. We anticipate higher stress and potential for marsquakes within intersegment zones and at graben tips.

In early 2019, NASA’s InSight lander successfully deployed a single three-component very broadband seismometer (VBB) on the surface of Mars to detect and characterize marsquakes. Using these data, we present a method to infer the source mechanisms of marsquakes from waveforms of P and S waves recorded at a single station. We show that the three events with the highest signal-to-noise ratio (SNR) and a robust distance estimate S0173a, (May 23rd 2019), S0235b, (July 27th 2019) and S0183a, (June 3rd 2019) are all likely the results of normal faulting, suggesting an extensional regime mainly oriented south-east north-west in the respective source regions, Cerberus Fossae and Orcus Patera. We quantify the uncertainty of our solutions by comparing results of a direct inversion with a grid-search method.

We quantitatively evaluate transducer-transducer one-source one-station active seismic waveform data, in order to monitor time-lapse changes of elastic and anelastic structure during deformation experiments in laboratory. The experiment data of dry and water-saturated sample are provided by Zaima and Katayama (2018, https://doi.org/10.1029/2018JB016377). A transducer receiver, at the mid-point of cylindrical rock sample, is located on the antipodal position of the transducer source, emitting compressional and shear waves. Due to the extremely underdetermined nature of inverse problem, we limit the number of unknowns to be four: global P- and S- wave velocities and their corresponding anelastic attenuation factors, which can represent the micro-cracks nucleation during the loading and before the appearance of the largest crack that causes the fracture. We first performed a trial-and-error search for a realistic boundary condition in three-dimensional seismic waveform modeling using spectral-element method, in order to fit the synthetic data with the observed waveforms. We then generated synthetic data for 6000 combinations of elastic and anelastic parameters, in order to conduct Monte-Carlo waveform inversion based on the cost functions using waveform misfit and zero-lag cross-correlation. We obtained the time-lapse changes in velocity and attenuation during the deformation, which are then linked to crack development. Compared with the wet experiment, the dry experiment has a larger change in both the velocity and attenuation. However, regardless of the configuration, global seismic wave speeds rise first and then decrease during the experiments. The quality factor shows roughly the same trend.