B-Value Mapping for Volcanic-Related Geothermal System: a Case Study of Nevado Del Ruiz Volcano, Colombia

Abstract

The Nevado del Ruiz Volcano (NRV) (Colombia) has two areas with geothermal potential located to the north and north-west of its crater which are highly seismically active. In the period of 2000 - 2018 thousands of volcano-tectonic events have been recorded beneath the volcano and within the two geothermal areas, with most earthquakes occuring at depths of 2-9 km and Md magnitudes up to 4.4.
Physical interpretations of subsurface processes related to volcano-geothermal activity can be performed by analyzing microseismicity information (hypocenters and magnitudes). The frequency-magnitude distribution of earthquakes in any region on Earth can be described by the Gutenberg-Ritcher relationship. This relationship is linear and from the slope, a common seismological parameter is estimated: the b-value. In the literature, high b-values have been associated with the presence of magmatic bodies, fluids migration, changes in fluid pressure, and high fracture density. Hence, the quantification of b-value and its uncertainty can be associated with the physics of subsurface mechanisms for earthquakes triggering. The aim of our study is to map b-values (2D and 3D) and delimit its anomalies with implications on the prospective geothermal areas of Nevado del Ruiz volcano. Potential mechanisms in the area are associated with fluid recharge from rainfall, variable stresses and changes in fluid pressures due to magma injection and fluid-phase transition (liquid water-to-vapor transitions).