• journal_title：Geology
• Contributor：Claudio Chiarabba ; Pasquale De Gori ; Enzo Boschi
• Publisher：Geological Society of America
• Date：2009-
• Format：text/html
• Language：en
• Identifier：10.1130/G25220A.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：37
• issue：1
• firstpage：67

In this study, we outline the space and time variations of body-wave velocities during one of the best-documented series of normal-faulting earthquakes, the 1997 Umbria-Marche sequence in central Italy. We show the first ever observations of rock fracturing and fluid overpressure propagation along a fault system by using space-time resolved variations of Vp/Vs anomalies (four-dimensional variations) that accompany earthquake migration and precede large aftershocks. The Vp/Vs increase observed before the mid-October earthquakes was related to a pore-pressure increase on fluid-filled cracks in the volume around the fault. We also document that such variations are measurable only by using S-and P-wave arrival times.