Reply to "Comment on 'Seismomagnetic Effects from the Long-Awaited 28 September 2004 M 6.0 Parkfield Earthquake' by M. J. S. Johnston, Y. Sasai, G. D. Egbert, and R. J. Mueller" by P. Varotsos and S. Uyeda

Abstract

The comment by Varotsos and Uyeda (2008) (VU hereafter) does not have much to do with our article, which reports electromagnetic data and their implications prior to, during, and following the 2004 M 6 Parkfield earthquake (EQ). In fact, our article did not include any extensive discussion of the possible flaws in the seismic electric signal (SES) approach to EQ prediction. The four main points VU discuss in their comment are from a summary sentence in the introduction that is preceded by the phrase “controversy about these (SES) results exists because (1), ... (2) ... (4),” where (1)–(4) are the specific points that VU list. We respond to each of these points in the following discussion. A final comment made by VU concerns our observation that SES-type signals are not seen in the data that we have. We could have provided more detailed evidence about the lack of SES in the months preceding the earthquake but see little point in including long data plots that show nothing. Note that all of these data are freely available from the Northern California Earthquake Data Center (NCEDC, www.ncedc.org, last accessed October 2007). In our article, we presented null results from sites above the Parkfield EQ rupture without extrapolating to the conclusion that SESs do not exist anywhere. In fact, Park et al. (2007) report additional data from 10–20 km lines over the entire region that also show no evidence for SES-type signals preceding the Parkfield EQ. Such signals were also not seen in 16 yr of previous monitoring with these lines (Park, 1991, 1997). Furthermore, no signals were seen in 2 yr of data on 10 km lines both along and within the fault and orthogonal to the fault a little farther to the north (Johnston, 1989). To suggest that all of these observations resulted from an …