A non‐accelerating foreshock sequence followed by a short period of quiescence for a large inland earthquake

Abstract

Using continuous waveforms recorded at a seismic station located in close proximity to the epicenter of the 2008 Iwate‐Miyagi inland earthquake, we conducted a detailed investigation of foreshock behavior. Calculation of cross‐correlation coefficients between the continuous waveform record and one of the officially recognized foreshock events revealed 20 micro foreshocks in addition to the two previously recognized foreshocks. Our analysis shows that all of the foreshocks occurred within the same general area relative to the main event. Over the two week period leading up to the Iwate‐Miyagi earthquake, foreshocks only occurred during the last 45 minutes, specifically over a 35 minute period followed by a 10 minute period of quiescence just before the mainshock. We found no evidence of acceleration of the foreshock sequence.