Theoretical assessment of the full_moment_tensor resolvability for receiver arrays used in microseismic monitoring

Abstract

An inversion of full moment tensors representing source mechanisms is becoming routinely used when interpreting microseismic monitoring. However, a stability of such inversion varies significantly for different receiver arrays. Unlike stability of location, which is hard to assess, the stability of inverted full moment tensor can be measured by a condition number. We tested three types of receiver arrays (dense surface array, dual borehole array and multi-borehole array) used in the microseismic monitoring and computed the theoretical stability of full moment tensor inversion from P-or P-and S-wave amplitudes at areas of interest. We analyzed a 3D distributions of the condition numbers and show that with surface and multi-borehole arrays of receivers we are capable of inverting stable source mechanisms for the events located at depths comparable to the maximum offset of receivers, but shallower events and the events at the depths of the borehole arrays are poorly constrained. This study provides a guidance for a quick prediction of source mechanism inversion quality. Computing condition numbers does not require any information about the data, it measures a theoretical quality of the moment tensor inversion. The computed condition numbers represent inversion for ideal dataset with the selected geometry.

Efficiency of Surface Monitoring Layouts for Retrieving Accurate Moment Tensors in Hydraulic Fracturing Experiments

“…Their layouts can be designed for various purposes: to enhance the signal-to-noise ratio (SNR) of recorded waves, to detect low-magnitude seismic events or to provide their accurate locations, energy, focal mechanisms or seismic moment tensors (MTs). Each of these goals needs its own specific sensor layout in order to produce the most accurate results, and many authors have conducted research on the sensor arrangement designed for these individual purposes (Anikiev et al, 2014;Chambers et al, 2010;Chen et al, 2019;Eaton & Forouhideh, 2011;Eisner et al, 2009Eisner et al, , 2010Eyre & van der Baan, 2017;Mesimeri et al, 2021;Pesicek, 2016;Schweitzer et al, 2011;Stane ˇk et al, 2017;Viegas et al, 2012;Wessels et al, 2011;Zhang et al, 2011).…”

“…In summary, the authors showed that the surface monitoring in field experiments and in situ studies could obtain accurate MTs of microseismic events, when a high number of sensors is used and the sensors densely cover the studied area. In some experiments, even thousands of sensors are used for data collection Eisner et al, 2010;Stane ˇk et al, 2014Stane ˇk et al, , 2017, when accurate MTs are to be determined. However, not all microseismic monitoring projects can use such a huge number of sensors.…”

Consistency of stress state, locations and source mechanisms of events induced by hydraulic fracturing: downhole monitoring

“…A well‐conditioned inversion has a low‐condition number and its result is stable, whereas an ill‐conditioned inversion has a high‐condition number and the resulting source mechanism is very sensitive to any small change in the input. Staněk, Eisner and Vesnaver () computed 3D distributions of condition numbers for our type of monitoring arrays. High‐condition numbers were found around and between the wells, but very low condition numbers were evaluated in the space where our events were located.…”