Passive Seismic Tomography

Geysers2009_Pvel_3km_depthPassive Seismic Tomography (PST)  is a technique developed in the early 80s by K. Aki and students at MIT to image the subsurface of the earth. PST is similar to a CAT scan of the human body, but instead of using X-rays, we use the elastic waves generated by microearthquakes as our energy source. Microearthquakes occur any where in the earth where the background stress field has been perturbed even to a small degree such that data from  a producing zone can be imaged from the surface using a well designed seismic network. Any moderately tectonically active region can be imaged using PST, where as a traditional 3D-seismic reflection survey may be impossible. Data collection happens over the course of a few weeks to months (depending on the level of activity in the area). PST is not a new technique and is well established; but only recently started to be used in the oil, gas, and mining industries to image the subsurface. ISTI can produce a complete 3D tomography image of the P and S wave velocity beneath the network once enough data have been collected. In addition, we can compute Vp/Vs ratios and hence Poisson’s ratio to establish the presence of fluids or geothermal activity within the zone of interest. Let ISTI develop a monitoring solution for your region of interest. We have the expertise, equipment, and staff to provide you with a complete end-to-end PST solution or if you already have a network running, we can use your data with our workflow to provide you with a complete 3D image.

TomoMapDepthSliceTomoSection_P_velTomoSection_PercentDiff

ISTI has developed an efficient workflow for processing data from a microseismic network to produce a 3D velocity image using our PST techniques. ISTI’s seismologists Ilya Dricker and Paul Friberg have been performing PST for industry using advanced techniques for many years (i.e., we use finite difference Eikonal equation solvers for ray tracing). ISTI works with leading researchers in this field to improve the algorithms in our workflow and to also provide high precision relative locations using double-differencing techniques (Waldhauser and Ellsworth, 2000) also using 3D velocity models.