Abstract
Compressional wave velocities (V p) in quartz aggregate were measured to quantify the effect of pore fluid (H2O) on V p at high pressure-temperature (P-T). Ultrasonic measurements were conducted on dry and wet quartz aggregate from room temperature to 500°C at 0.5 GPa using a piston cylinder apparatus. The experiment showed a 4% decrease in measured V p in quartz aggregate with increasing H2O content to 1 wt.%, whereas the temperature derivative of V p (∂V p/∂T = -2.8 to -4.9 × 10-4 km s-1°C-1) in wet quartz aggregate remained almost the same as for the dry quartz aggregate (∂V p/∂T = -5.2 × 10-4 km s-1°C-1). Our high-pressure, high-temperature experiments show that a small amount of pore fluid (0.4 to 1.0 wt.% H2O) can significantly reduce V p under the P-T conditions of the middle crust.
Highlights
Compressional wave velocities (Vp) in quartz aggregate were measured to quantify the effect of pore fluid (H2O) on Vp at high pressure-temperature (P-T)
Our results demonstrate that the compressional wave velocity decreases significantly at 1 wt.% H2O under the P-T conditions of the middle crust
Our results show that the addition of 0.4 to 1.0 wt.% H2O into the quartz aggregate causes a velocity drop of 3% to 4% at the pressures and temperatures of the middle crust (0.5 GPa, 25°C to 500°C), which suggests that one possible reason for low seismic velocities (−5%) is 1 wt.% H2O fluid-filled rock in the hypocentral zone
Summary
Compressional wave velocities (Vp) in quartz aggregate were measured to quantify the effect of pore fluid (H2O) on Vp at high pressure-temperature (P-T). Ultrasonic measurements were conducted on dry and wet quartz aggregate from room temperature to 500°C at 0.5 GPa using a piston cylinder apparatus. The experiment showed a 4% decrease in measured Vp in quartz aggregate with increasing H2O content to 1 wt.%, whereas the temperature derivative of Vp (∂Vp/∂T = −2.8 to −4.9 × 10−4 km s−1°C−1) in wet quartz aggregate remained almost the same as for the dry quartz aggregate (∂Vp/∂T = −5.2 × 10−4 km s−1°C−1). Our high-pressure, high-temperature experiments show that a small amount of pore fluid (0.4 to 1.0 wt.% H2O) can significantly reduce Vp under the P-T conditions of the middle crust
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