Field observations and numerical simulations on the role of local structures and seismic source characteristics in the in uence of external earthquakes in volcanic and hydrothermal activity

Abstract

Earthquakes can trigger volcanic and hydrothermal activity at a large distance range and a wide time window. While advances in observations in the last two decades have helped to establish that there exist a causal connection between earthquakes and volcanism, the underlying physical mechanisms that control such interaction are not completely understood. <br /> In this thesis I study the influence of earthquakes in volcanic and hydrothermal zones using field observations and numerical simulations. The observations come from the data retrieved in a field campaign at Nevados de Chillán volcano, located in central-south Chile. This composite volcanic/hydrothermal system recorded an interesting response to two large aftershocks of the Maule earthquake, of magnitudes MW = 6.1 and MW = 7.1, with both of them located about 200 km from the system. The complex recorded an increase in local seismicity for the first, smaller event, and a slight decrease in seismicity for the larger earthquake. <br /> To have a better understanding of the underlying physical mechanisms that control the earthquake influence in a volcanic/hydrothermal system I used numerical sim- ulations to quantify the dynamic and static changes induced by the earthquake in simple systems composed by fluid reservoirs connected to geological faults. Results show that, while the earthquake characteristics dominate its influence in a volcanic region, the local structures play a very important role, altering both the static and dynamic changes induced by the earthquake. The results unveil a far more complex earthquake impact in a volcanic/hydrothermal system that it has been considered so far, with local structures, such as fluid reservoirs and geological faults, being impor- tant players in the modulation of the earthquake influence on the system. Finally, I present the results of a simulation of the Nevados de Chillán response to the two large aftershocks of the 2010 Maule earthquake. Results show that the sum of the earthquake characteristics with the geometry of the local structures are key to un- derstand the different effects that the two events have in the volcanic/hydrothermal system, with the MW = 6.1 being more important at a fluid level, which is congruent with the field observations. <br /> The results presented in this thesis support the idea of a complex relationship be- tween earthquakes and volcanic/hydrothermal activity, in which both the earthquake characteristics and the local structures of the volcanic/hydrothermal system must be taken into account.