Heat signature on the Chelungpu fault associated with the 1999 Chi‐Chi, Taiwan earthquake

Abstract

[1] We have made observations of a heat signature that is associated with the frictional heat generated at the time of faulting for a large earthquake. Temperature measurements in a borehole that intersects the Chelungpu fault at a depth of about 1100 m, show a small increase near the fault even six years after the earthquake. The temperature signature has a symmetric shape with a width of about 40 m and is centered on the fault that slipped about 5 m during the 1999 Chi-Chi, Taiwan earthquake. The small amplitude of 0.06°C for the observed temperature anomaly indicates a very low level of friction that generated heat at the time of the earthquake.

Extreme hydrothermal conditions at an active plate-bounding fault

“…Drilling has revealed that heat generated by > 50 m of slip during the Tohoku-Oki 2011 earthquake (moment magnitude M w = 9.0) produced only a small temperature anomaly, requiring an average friction coefficient during slip of < 0.1 (ref. 10); similar results were found after the Wenchuan 2008 and Chi-Chi 1999 earthquakes 11,12 . Plate boundary faults must, therefore, be composed of materials that are mechanically weak on long timescales, even if weakness is a transient phenomenon during movement.…”

“…Drilling studies have taken place in response to earthquakes of M w = 6.9-9.0 in Japan, Taiwan, China and the USA 8,[10][11][12][18][19][20][21] , and the results do not reveal anomalous temperatures or fluid pressures (Fig. 1).…”

Does hydrologic circulation mask frictional heat on faults after large earthquakes?

“…Studies of processes that may mask or dissipate the frictional heat signal have focused on steady state topographically driven or buoyancy-driven groundwater flow [Williams and Narisimhan, 1989;Saffer et al, 2003;Fulton et al, 2004] and the effects of heterogeneous thermal properties [Tanaka et al, 2007;Fulton and Saffer, 2009a]. One candidate for obscuring a frictionally generated thermal signal that has not been fully explored is transient groundwater flow following an earthquake [e.g., Kano et al, 2006;Scholz, 2006].…”

“…This magnitude of friction is hypothesized to generate large thermal anomalies on natural faults with large slip rates and/or large total displacements, assuming hydrostatic pore pressure. Curiously, analysis of surface heat flow data [e.g., Brune et al, 1969;Lachenbruch and Sass, 1980;Wang et al, 1995] and subsurface temperature profiles [Yamano and Goto, 2001;Kano et al, 2006;Tanaka et al, 2006Tanaka et al, , 2007 that cross fault zones do not show substantial, unequivocal anomalies from frictional heating. These observations prompt two questions: (1) could the frictional resistance be as large as expected from Byerlee's law and hydrostatic pore pressure, but the heat signal is masked or dissipated by other processes?…”

Drilling Into Faults Quickly After Earthquakes

“…Temperature profiles across the fault are the most direct way to quantify coseismic friction [e.g., Tanaka et al, 2006;Kano et al, 2006]. Because most frictional resistance is dissipated as heat, any temperature increase on the fault at the time of the earthquake is potentially interpretable as a cumulative measure of frictional heat generated during slip [Lachenbruch and Sass, 1980].…”