Ph.D. Research Proposal Passive Seismic Imaging

The passive seismic imaging problem For 35 years, the theory for passively imaging the subsurface of the earth has been available to the seismic exploration community. The proof that the information contained in a transmission record is fundamentally related to the reflection seismic experiment allows for the manufacture of seismic cross-sections of the earth without the use of an energy source. While this theory has stood in the literature, it has not graduated to the seismic toolbox as a practical methodology available for answering subsurface questions in the exploration community. According to Claerbout’s 1968 article, a seismogram recorded at the surface due to a buried source (transmission record) carries the same information as the recording from a surface source and receiver at the same location. The relationship is shown as the auto-correlation of the transmission record being equivalent to the reflection seismogram record. Thus, without requiring the application of a source, this relationship allows for the manufacture of subsurface images with conventional seismic processing techniques by first correlating the passive seismic recordings. These stations can be distributed across the surface of the earth, left to record the ambient noise-field, and then the data retrieved for processing without mobilizing a synthetic source or waiting for earthquake events. Importance to the scientific community The manifold utility of imaging the subsurface has been proved repeatedly in engineering, characterization, monitoring, and exploration applications. Academic interest in imaging the subsurface abounds with investigations ranging from a few kilometers depth to the crustal scale. Seismic investigation of the near and deep subsurface finds ready customers in any one or several of the above communities with existing reflection experiment methods. The practicalities and costs of reflection seismic data acquisition however, particularly the mobilization of people and equipment to new and removed sites, sometimes makes acquiring a survey, or repeated surveys, undesirable or impossible. Specifically, the man-hours, permitting, and materiel associated with the seismic source are burdensome. Geophones, however, are fairly inexpensive, can be laid out and retrieved quickly, and even fixed in the field permanently if usable information can be routinely produced. The passive seismic imaging experiment, capitalizing on the ambient noise-field in the earth, has the potential to alleviate the problems and costs of source detonation by not requiring the application of a source at all. This could be of immense utility to academic earth investigators who are typically cash constrained. Not needing an active source could greatly increase the number of sites available for any community to investigate as the permitting process will be much easier without the introduction of heavy source trucks or explosives. Last, with an instrumented monitoring program deployed in the field, repeated images of the subsurface collected over time can be of imPassive Seismic Imaging Ph.D. Proposal 3 Artman mense value to the monitoring of temporal processes in the subsurface. The most obvious application is to fluid flow (water, hydrocarbons, contaminates), though structural monitoring of tectonically active regimes would also be applicable. Further, if the methodology is shown effective for large scale deployments such as the Santa Clara Valley Seismic Experiment (to be introduced later) it can add a previously unexplored look into the subsurface using available data sets or proposed deployments. Proposal to address the validity of the method I propose to answer whether or not the passive seismic experiment as outlined below can be used as a practicable methodology for subsurface imaging and/or monitoring. Answered in the affirmative, I will delineate the range of subsurface parameters necessary to the success of this type experiment as well as estimate the sensitivity of the methodology to common earth parameter ranges. Conversely, if the various investigations to be described fail, it will be important to fully understand the reasons underlying its failure so as to put to rest the question of applicability of this methodology to the exploration seismic community. Toward answering this question, the data driven nature of this department and this science makes the acquisition of passive seismic data sets imperative to accomplish this goal. Thus far, I have secured several firm commitments to acquire exploration oriented data sets and more efforts are still pending. Data from the solar and earth seismology and volcanic monitoring groups are also available for manipulation. Finally, I have collected a small scale data set on the beach at Moss Landing. The following list reflects the specifics of each: • 1000 channel linear acquisition riding on a planned mobilization in Southern California by the United States Geological Survey (USGS). Confirmed, September 2002 • 1000 channel linear acquisition riding on a planned mobilization in Santa Clara Valley, by the United States Geological Survey (USGS). Confirmed, September 2002 • ∼ 10K channel areal acquisition riding on a planned mobilization in South Texas by the Compagnie Générale de Géophysique (CGG). Confirmed, August 2002 • 65536 channel areal acquisition around a solar flare on the sun by the Stanford-Lockheed Institute for Space Research. In-house • 48 channel areal acquisition within the Santa Clara Valley by the USGS. In-house • 72 channel areal acquisition over buried objects and water table on Moss Landing beach by me. In house • 960 channel parallel linear acquisition of ocean-bottom cable (OBC) passive seismic by Petroleum Geo-Services previously acquired. In transit • Unspecified linear acquisition by Petroleum Geo-Services. Pending Passive Seismic Imaging Ph.D. Proposal 4 Artman • 100 channel volumetric deployment of monitoring stations throughout the INCO nickel mine in Ontario, Canada. Pending • Unspecified areal acquisition by Saudi Aramco. Pending • Various array strategy experiments publicly available in international seismic data libraries. Available With these data sets, I will be able to test the efficacy of the passive imaging premise for two and three dimensions. The availability of these data sets is immensely important to the success of this research. Furthermore, the availability of several data sets of such widely varying nature will facilitate a thorough investigation into the practicality and use parameters of this novel seismic tool. This research will conclude upon the understanding of how and when to use the passive seismic experiment or the reason(s) that it fails us.