Energy Budget of Intermediate‐Depth Earthquakes in Northern Chile: Comparison With Shallow Earthquakes and Implications of Rupture Velocity Models Used

We calculate well-resolved corner frequencies and radiated energies for a set of 96 earthquakes divided into two clusters located in the same tectonic setting but with different depths in northern Chile. Fifty-three shallow events with a mean depth of 20 km are analyzed, along with 43 intermediate-depth earthquakes with a mean depth of 110 km. We deduce and compare their static (stress drop Delta sigma) and dynamic (rupture energy E-G and radiation efficiency eta(R)) source parameters and test the implications of different common assumptions on their depth dependence, such as stress drop invariance, strain drop invariance, or constant rupture velocities. Our data show that, in this zone of Chile, most of these models imply higher rupture velocities at depth than for shallow earthquakes. In these cases, high stress drop, high fracture energy release rate, and higher radiation efficiency are observed for intermediate-depth earthquakes, suggesting short and impulsive ruptures. Plain Language Summary Seismicity deeper than 60 km represents only 20% of the recent observed seismic activity in Chile but can produce real destruction, such as the magnitude 7.8 Tarapaca earthquake in 2005. The physical mechanisms by which these earthquakes initiate and propagate still remains unclear, and quantitative observations and analyzes are needed to understand them better. This study shows that the energy released is used differently in intermediate-depth earthquakes than in the shallow earthquakes in the northern part of Chile. By analyzing the model properties needed to explain these shallow and deep earthquakes, we show that these differences are strongly dependent on how fast the earthquake occurs. We then compare the influence of this rupture speed on how our set of earthquakes initiates and show that the intermediate-depth earthquakes in northern Chile seem to start more quickly with shorter bursts of energy than the shallow earthquakes.