We propose to establish theoretical frameworks that conceptualize propagation of difference waves, defined as the wave field difference between the repeated sources, and use difference wave fields to effectively image temporal change of properties in the media. We also propose to study possible temporal changes of seismic properties globally using dense arrays and earthquake doublets, and to explore the relationship of temporal changes of seismic properties with many interesting geological phenomena, such as earthquake process, fault zone behavior, glacier melting, volcano eruption and geothermal activities. The conceptualization we propose would make experiment design and resolution analysis straightforward and overcome many challenging issues in the current methods for determining temporal property changes in the medium. The conceptualization also makes it possible to pinpoint and quantify temporal changes inside the medium. During the course of research, we will also formulate empirical procedures to handle the situation of imperfect source repeatability in the real data processing.
Using seismic or ultrasonic waves to probe temporal change in the medium is an important topic in ultrasound experiments, civil engineering, medical imaging, and geological sciences. In geological sciences, probing temporal medium change has not only started to provide fundamental insights into physics of many geophysical phenomena, such as earthquake nucleation, fault zone damage and healing process, volcano activities, stress build-up in the crust and the thermo-chemical processes in the top of the Earth?s inner core, they have also become a practical and effective tool for monitoring evolution of oil fields and underground carbon sequestration.
