A Comprehensive Stress Drop Map From Trench to Depth in the Northern Chilean Subduction Zone

We compute stress drops for earthquakes in Northern Chile recorded between 2007 and 2021. By applying two analysis techniques, (a) the spectral ratio (SR) method and (b) the spectral decomposition (SDC) method, a stress drop map for the subduction zone consisting of 51,510 stress drop values is produced. We build an extended set of empirical Green's functions (EGF) for the SR method by systematic template matching. Outputs are used to compare with results from the SDC approach, where we apply cell-wise obtained global EGF's to compensate for the structural heterogeneity of the subduction zone. We find a good consistency of results of the two methods. The increased spatial coverage and quantity of stress drop estimates from the SDC method facilitate a consistent stress drop mapping of the different seismotectonic domains. Albeit only small differences of median stress drop, strike-perpendicular depth sections clearly reveal systematic variations, with earthquakes at different seismotectonic locations exhibiting distinct values. In particular, interface seismicity is characterized by the lowest observed median value, whereas upper plate earthquakes show noticeably higher stress drop values. Intermediate depth earthquakes show comparatively high average stress drop and a rather strong depth-dependent increase of median stress drop. Additionally, we observe spatio-temporal variability of stress drops related to the occurrence of the two megathrust earthquakes in the study region. The presented study is the first coherent large scale 3D stress drop mapping of the Northern Chilean subduction zone. It provides an important component for further detailed analysis of the physics of earthquake ruptures. Stress drop is the released stress on a fault during a seismic rupture. We compute stress drops for earthquakes in northern Chile recorded between 2007 and 2021. By applying two different analysis techniques, (a) the spectral ratio method and (b) the spectral decomposition method, a stress drop map for the subduction zone consisting of 51,510 stress drop values is produced. We find a good consistency of results of the two methods. The good spatial coverage and quantity of stress drop estimates allow a consistent stress drop mapping of the seismically active domains. Although differences of median stress drops are relatively small, the depth section clearly reveals systematic variations, with earthquakes of different classes. In particular, interface seismicity is characterized by the low median values, whereas upper plate earthquakes show noticeably higher stress drops. Intermediate depth earthquakes show comparatively high average stress drop and depth-dependence. Additionally, we observe variability of stress drops related to the occurrence of the two megathrust earthquakes in the study region. The here presented study is the first large scale 3D stress drop mapping of the Northern Chilean subduction zone. It provides an important component for further analysis of the physics of earthquake ruptures. A comprehensive stress drop distribution with more than 51,000 stress drop estimates for the Northern Chilean Subduction Zone is computedSystematic stress drop variations between upper plate, interface and intermediate depth seismicity are revealedReliability and comparability of results are increased by using two methods, the spectral ratio and the spectral decomposition approach