In many geoscientific, material science, and engineering applications it is of importance to estimate a representative bulk seismic velocity of materials or to locate the source of recorded seismic or acoustic waves. Such estimates are necessary in order to interpret industrial seismic and earthquake seismological data, for example, in nondestructive evaluation and monitoring of structural materials, and as an input to rock physics models that predict other parameters of interest. Bulk velocity is commonly estimated in laboratories from the time of flight of the first‐arriving wave between a source and a receiver, assuming a linear raypath. In heterogeneous media, that method provides biased estimates of the bulk velocity, and of derived parameters such as temporal velocity changes or the locations of acoustic emissions. We show that coda wave interferometry (CWI) characterizes changes in the bulk properties of scattering media far more effectively on the scale of laboratory rock samples. Compared to conventional methods, CWI provides significant improvements in both accuracy and precision of estimates of velocity changes, and distances between pairs of acoustic sources, remaining accurate in the presence of background noise, and when source location and velocity perturbations occur simultaneously. CWI also allows 3‐D relative locations of clusters of acoustic emissions to be estimated using only a single sensor. We present a method to use CWI to infer changes in both P and S wave velocities individually. These innovations represent significant improvements in our ability to characterize the evolution of properties of media for a variety of applications.

A novel source location method based on coda wave interferometry (CWI) was applied to a microseismic data set of mining-induced events recorded in Nottinghamshire, England. CWI uses scattered waves in the coda of seismograms to estimate the differences between two seismic states. We used CWI to estimate the distances between pairs of earthquake locations, which are then used jointly to determine the relative location of a cluster of events using a probabilistic framework. We evaluated two improvements to this location technique: These account for the impact of a large difference in the dominant wavelength of a recording made on different instruments, and they standardize the selection of parameters to be used when implementing the method. Although the method has been shown to produce reasonable estimates on larger earthquakes, we tested the method for microseismic events with shorter distinguishable codas in recorded waveforms, and hence, fewer recorded scattered waves. The earthquake location results are highly consistent when using different individual seismometer channels, showing that it is possible to locate event clusters with a single-channel seismometer. We thus extend the potential applications of this cost-effective method to seismic events over a wider range of magnitudes.

A wide range of applications requires the relative locations of sources of energy to be known accurately. Most conventional location methods are either subject to errors that depend strongly on inaccuracy in the model of propagation velocity used or demand a well-distributed network of surrounding seismic stations to produce reliable results. A new source location method based on coda-wave interferometry (CWI) is relatively insensitive to the number of seismic stations and to the source-to-station azimuthal coverage. Therefore, it opens new avenues for research, for applications in areas with unfavorable recording geometries, and for applications that require a complementary method. This method uses CWI to estimate distances between pairs of seismic events with a similar source mechanism recorded at the same station. These separation estimates are used to solve for the locations of clusters of events relative to one another within a probabilistic framework through optimization. It is even possible to find the relative locations of clusters of events with one single-channel station. Given these advantages, it is likely that one reason that the method is not used more widely is the lack of reliable code that implements this multistage method. Therefore, we have developed a well-commented MATLAB code that does so, and we evaluate examples of its applications. It can be used with seismic data from a single-station channel, and it enables data recorded by different channels and stations to be used simultaneously. It is therefore possible to combine data from permanent yet sparse networks and from temporary arrays closer to the source region. We use the code to apply the location method to a selected data set of the New Ollerton earthquakes in England to demonstrate the validity of the code. The worked example is provided within the package. A way to assess the quality of the location results is also provided.

No abstract

No abstract