| Despite the large amount of literature published dealing with the relationship between electromagnetic (EM) signals and pre-seismic processes in the earth's crust, there is still no definitive proof that the two are connected. In this dissertation I introduce additional new data sets and analyses to the already existing, yet insufficient, collection of ULF (ultra-low frequency: 0.01–10 Hz) EM observations prior to major earthquakes and fault creep. The purpose of my investigation is not only to clarify whether there is a relationship between ULF EM phenomena and earthquakes, but to gain insight into whether there are processes in the earth's crust that can give rise to observable ULF EM signals, and, if so, how this might contribute to our knowledge of the physics of earthquakes.; I addressed the difficulty of measuring EM signals close to large earthquakes by developing a transportable system with which to measure 3-component magnetic field and 2-component electric field ULF signals for deployment in the epicentral region of a major earthquake immediately following a main shock. I deployed two of these transportable systems in the immediate aftermath of the 1999 M = 7.1 Hector Mine earthquake in southern California and found no evidence for ULF-EM signals associated with M ≈ 3.5 earthquakes despite the existence of numerous ULF-EM signal changes at the time of the earthquakes. I also found no post-seismic ULF response similar to that seen following the 1989 Loma Prieta earthquake which suggests that the anomalous Loma Prieta signals must have been controlled by something other than the seismic moment.; In addition, recordings ∼2 km away from the epicenter of the 1998 M = 5.1 San Juan Bautista, California earthquake show no obvious ULF anomalies prior to the earthquake. I also show that, in contrast to a previous report, magnetic field changes do not occur clearly prior to episodic fault creep along the San Andreas fault at a measurement resolution of ∼0.01 nT in the ULF range. My results constrain previously proposed EM signal generation mechanisms and provide guidelines according to which future EM-earthquake experiments may be designed. |
