Amplitude Source Location Method With Depth‐Dependent Scattering and Attenuation Structures: Application at Nevado del Ruiz Volcano, Colombia

Abstract

AbstractThe amplitude source location (ASL) method, which uses high‐frequency amplitudes based on the assumption of isotropic radiation of S waves, was tested with envelope waveforms simulated from depth‐dependent scattering and attenuation structures at Nevado del Ruiz volcano, Colombia. Our test results indicate that estimated ASLs are more accurate when a two‐layer attenuation model is used than when a homogenous attenuation model is used, as has commonly been done in previous studies. We applied the ASL method with a two‐layer attenuation model to the high‐frequency (5‐10 Hz) band of volcanotectonic (VT) earthquakes, long‐period (LP) and very long period (VLP) events, and tremor recorded in 2016 at Nevado del Ruiz. Results indicate that the differences between ASLs and VT earthquake hypocenters (determined using onset arrival times) were smaller for a two‐layer model compared to a homogeneous model. Our determined ASLs for LP and VLP events and tremor were distributed along a NW‐dipping plane beneath the summit crater, near and above a region with high P to S wave velocity ratios that has been interpreted as shallow magma storage. This plane may represent weak zones along the Palestina fault system. Our results suggest that LP and VLP events and tremor occur during magma ascent along the fault system. This study demonstrates that the ASL method with a depth‐dependent attenuation model is useful to improve the accuracy of estimated source locations for volcanoseismic signals.