Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the V S,30 at a site. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results. The present guidelines provide practical Electronic supplementary material The online version of this article
11We characterise the aftershock sequence following the 2016 Mw=7.8 Pedernales earthquake. 12More than 10,000 events were detected and located, with magnitudes up to 6.9. Most of the 13 aftershock seismicity results from interplate thrust faulting, but we also observe a few normal 14 and strike-slip mechanisms. Seismicity extends for more than 300 km along strike, and is 15 constrained between the trench and the maximum depth of the coseismic rupture. The most 16 striking feature is the presence of three seismicity bands, perpendicular to the trench, which 17 are also observed during the interseismic period. Additionally, we observe a linear 18 dependency between the temporal evolution of afterslip and aftershocks. We also find a 19 temporal semi-logarithmic expansion of aftershock seismicity along strike and dip directions, 20 further indicating that their occurrence is modulated by afterslip. Lastly, we observe that the 21 spatial distribution of seismic and aseismic slip processes is correlated to the distribution of 22 bathymetric anomalies associated with the northern flank of the Carnegie Ridge, suggesting 23 that slip in the area could be influenced by the relief of the subducting seafloor. To explain 24 our observations, we propose a conceptual model in which the Ecuadorian margin is subject 25 to a bimodal slip mode, with distributed seismic and aseismic slip mechanically controlled by 26 the subduction of a rough oceanic relief. Our study sheds new light on the mechanics of 27 subduction, relevant for convergent margins with a complex and heterogeneous structure 28 such as the Ecuadorian margin. 29
In this paper, we introduce a fourth-order leapfrog time scheme combined with a high-order discontinuous Galerkin method for the solution of the elastodynamic equations. The time discretization, obtained via a simple construction based on Taylor developments, provides an accurate scheme for the numerical simulation of seismic wave propagation. Results of the propagation of an eigenmode allow a numerical study of stability and convergence of the scheme for both uniform and non structured meshes proving the high level of accuracy of the method. The robustness of the scheme in the heterogeneous case is studied and we also examine the propagation of an explosive source in a homogeneous half-space. Un schéma d'ordré elevé de type Galerkin discontinu pour la propagation d'ondesélastiquesondesélastiques Résumé : On présente un schéma saute-mouton en temps d'ordre quatre com-binébinéà une méthode de type Galerkin discontinu d'ordré elevé en espace pour la résolution deséquationsdeséquations de l'´ elastodynamique. La discrétisation temporelle, simplement déduite de développements de Taylor, permet d'obtenir un schéma précis pour la simulation numérique de la propagation d'ondes sismiques. UnéUné etude numérique de la stabilité et de la convergence du schéma, via l'´ etude de la propagation d'un mode propre utilisant des maillages uniformes et non struc-turés, prouve la précision de la méthode. La robustesse du schéma estétudiéeestétudiée dans le cas d'un milieu hétérogène et l'on s'intéressé egalementàegalementà la propagation d'une source explosive dans un demi-espace homogène.
Abstract. The use of distributed acoustic sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves' apparent phase velocity, which varies for different seismic phases ranging from fast body waves to slow surface and scattered waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body waves compared to slow scattered waves and ambient noise and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P and S wave records. The demonstrated ability to resolve source parameters using P waves on horizontal ocean-bottom fibers is key for the implementation of DAS-based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore earthquakes, including those capable of generating tsunami.
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