Project report and algorithms for optimizing acquisition layout and frequency

D2.7. Project report and algorithms for optimizing acquisition layout and frequency. We evaluate the capability of 3D finite difference codes to model Distributed Acoustic Sensors (DAS) at reservoir scale for monitoring of CO2 sequestration. This work builds on previous DigiMon deliverables: 1.3 - DAS synthetic dataset (Baird et al, 2020b) and 2.1 - Framework for forward modelling of the DigiMon data (Vandeweijer et al, 2021). The goals of this work include 1) evaluation of the computational load and trade-offs needed to model Distributed Acoustic Sensing (DAS) signals from a 3D (~14x14x3 km) model of a CO2 sequestration reservoir; 2) sensitivity of various DAS deployment models (borehole versus surface); 3) comparison of DAS (linear and helical) with respect to geophones for both vertical and surface installations; and 4) measurements of possible induced seismicity with DAS

Data from lab-scale experiments of fibre optic vibration measurement

Understanding the exact nature of the coupling of the optical fiber in response to seismic waves in a variety of settings is key to quantitative interpretation and modelling of seismic data recorded by Distributed Acoustic Sensors (DAS). While field experiments are very useful for gaining understanding their interpretation is complicated by variations in the conditions along the fibre, such how “straight” the fibre is at a given location, and the properties of the surrounding material. Lab-scale experiment can be useful for investigating specific parameters, since they allow for precise control over the local conditions over short lengths of fibre. This activity works towards the establishment of a lab-scale test bed for characterizing fibre optic response to seismic disturbancesData from lab-scale experiments of fibre optic vibration measurementpublishedVersio

震源と地震動における地表断層地震と地中断層地震との相違

In previous work, we have shown that the ground motions from crustal earthquakes that break the ground surface are weaker than the ground motions from buried faulting crustal earthquakes. In this paper, we describe differences in kinematic and dynamic source parameters that may give rise to these differences in ground motion levels. From kinematic rupture models, we show that the slip velocity of surface faulting earthquakes is less that the slip velocity of buried faulting earthquakes. From dynamic rupture models, we infer that rupture in the shallow part of fault (upper few km) is controlled by velocity strengthening, with larger slip weakening distance Dc, larger fracture energy, larger energy absorption from the crack tip, lower rupture velocity, and lower slip velocity than at greater depths on the fault. Dynamic rupture modeling using these properties results in lower ground motions for surface faulting than for buried faulting events, consistent with the observations

Estudio de la estabilidad y dispersión del problema de propagación de ondas sísmicas en 2-D utilizando el método de diferencias finitas generalizadas

AbstractThis paper shows the solution to the problem of seismic wave propagation in 2-D using generalized finite difference (GFD) explicit schemes. Regular and irregular meshes can be used with this method.As we are using an explicit method, it is necessary to obtain the stability condition by using the von Neumann analysis. We also obtained the star dispersion formulas for the phase velocities for the P and S waves, as well as the ones for the group velocities.As the control over the irregularity in the mesh is very important in the application of this method, we have defined an index of irregularity for the star (IIS) and another for the cloud (IIC), analyzing its relationship with the dispersion and time step used in the calculations