Microseismic Events Detection And Location Based On Seismic Array

Seismic arrays were first established to detect and identify nuclear explosions in 1950s,and then provided a possibility of achieving small events detection and resolving the fine structure of the Earth's interior.One of the main advantages of a seismic array compared to a single seismic station is that the signal-to-noise ratio(SNR)is improved due to the summation of the signals from the individual records at the array station.The second advantage is that seismic arrays can also determine the direction of seismic signals as well as having the low SNR signal detected.In this thesis,array techniques are applied to the microseismic detection and location of shale-gas hydrofracturing induced seismicity,as well as seismicity in northern Chilean subduction zone.For shale-gas hydraulic fracturing monitoring,detection of microseismic events is of vital importance for crack delineation.However,it still remains a great challenge because microseismic events have relatively small amplitudes and low signal-to-noise ratios.Compared with the traditional short-time-average to long-time-average(STA/LTA)detector,match and locate algorithm(M&L)can effectively achieve the detection and location of small events based on the waveform similarity between templates and detecting events,as well as the waveform coherency among stations.We apply M&L to detect microseismic events induced by the hydrofracturing of a shale-gas reservoir.The number of events detected is three times more than the number of template,which previously were derived from an improved short-time-average to long-time-average algorithm(STA/LTA).And the location of these events are determined at the same time with detection.Then a small events detection procedure for three arrays based on FK analysis has been developed to detect the seismicity in northern Chilean subduction zone.More than twice as many events are detected based on array analysis compared with catalog events.Moreover,suspected non-volcanic tremor signals is initially detected.The detection and location results of different array analysis methods in different types of events show that the detection and location of weak events based on arrays is an effective method.