A variation of the collapsing method to delineate structures inside a microseismic cloud

We describe a modification to the collapsing method, a technique that aims to find the simplest structures in a cloud of microearthquakes by utilizing the statistical uncertainties in the data. In the modified collapsing meth od, the movements of the locations are dependent on the shape of the distri bution of the locations within the confidence ellipsoid, and not just the p osition of the center of gravity, as is the case in the original method. Ad ditionally, whereas the original collapsing method implicitly assumes that all locations belong to point structures, in this modified version three ty pes of structure are considered: point, line, and plane. Principal componen t analysis of the locations is used to evaluate to which type of structure each location most probably belongs. The modified technique has been applie d to microseismic events associated with hydraulic stimulation at the Fento n Hill HDR Field, New Mexico, and known small-scale structures were imaged.