Introduction

The primary objective of the UC Berkeley electromagnetic (EM) monitoring array is to identify EM fields that might be associated with earthquakes. For an overview of the sites and instruments see Kappler et al. 2006. We have continued to analyze the data from the Parkfield-Hollister (PKD-SAO) electromagnetic monitoring array taken during the four-year time window January 2002 to December 2005. We stress that although the data have been collected since 1996, large gaps in data acquisition due to lack of funding for array maintenance, together with incomplete documentation of when array sensors were swapped out and/or repaired, has made it difficult to examine small variations in parameters derived from array data. The focus this year has been on identifying those components of the EM fields observed which are coherent with natural micropulsations of earth's magnetosphere. The residuals obtained by removing this known natural source reflect the EM activity which is incoherent with the dominant natural fields. The method of separation is based upon projecting the observed data onto the eigenvectors of the robust estimated spectral density matrix (SDM).

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