Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT24] Attenuation from crust to core: in situ experiments, observaions and implications

Sun. May 26, 2019 9:00 AM - 10:30 AM A09 (TOKYO BAY MAKUHARI HALL)

convener:Konishi Kensuke(Institute of Earth Sciences, Academia Sinica), Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Takashi Yoshino(Institute for Planetary Materials, Okayama University), Alexandre Schubnel(CNRS), Chairperson:Kensuke Konishi(Institute of Earth Sciences)

9:00 AM - 9:15 AM

[SIT24-01] Anomalous Vp/Vs Ratios at Seismic Frequencies Might Evidence Highly Damaged Rocks in Subduction Zones

*Alexandre Schubnel1, Lucas Pimienta2, Marie Violay2, Jérome Fortin1, Hélène Lyon-Caean1 (1.Laboratoire de Géologie, ENS PARIS, 2.EPFL, Switzerland)

Keywords:VP/Vs ratio, undrained / drained deformation, fluids

Unusually high compressional (P) to shear (S) wave velocity ratios (Vp/Vs) were measured at different subduction zones and interpreted as fluid-pressurized regions. Because no laboratory data reported such high values in isotropic rocks, mineralogical or anisotropic constrains were assumed. However, fluid-saturated rocks’ Vp/Vs is a frequency-dependent property so that standard laboratory measurements cannot be directly upscaled to the field. Using a new methodology, we measured the property in the elastic regime relevant to field measurements for diverse lithologies. We obtained extreme Vp/Vs values, consistent with those reported at seismic frequency in the field. Consistently with a model, it shows that if high fluid pressure is a key factor, anomalous Vp/Vs values could evidence intense degrees of microfracturation in isotropic rocks, whichever its mineralogical content. The permeability of these regions could be larger than 10-16 m2.