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The Southern Patagonian Icefield (SPI) lies above an area of slow convergence between Antarctic and South-America plates, where limited seismicity is recorded by global and regional seismic networks. To understand the seismic behavior of this zone, we analyze two years of continuous broad-band data recorded by 27 seismometers, deployed around the SPI. Substantial ice loss coupled with the unusually low viscosity of the underlying mantle is causing a rapid uplift. Our findings indicate that most of the seismicity occurs in the upper crust , likely associated with the (re)activation of regional compressive structures. However, earthquakes immediately beneath the SPI generally are shallower and show normal or strike-slip faulting. We suggest that this activity is promoted as a response to the crustal relaxation after rapid ice removal of SPI. The almost complete absence of interplate and intraslab events is consistent with a locked megathrust fault interface, highlighting the similarity of this region with the Cascadia subduction zone. • Shallow seismicity is observed in the majority in the area of southern Patagonia Icefield. • The inferred stress suggests the solid earth response to mass loss from the icefield as the major cause. • The almost complete absence of interplate earthquakes suggests that the megathrust may be locked. [ABSTRACT FROM AUTHOR]

In the South‐Central Andes, the crustal structures driving the tectonic evolution of the Andean Cordillera remain unresolved. So far, most seismological studies focused on the subduction interface, leaving crustal seismicity and its relationship with crustal deformation and Andean volcanism mostly unconstrained. However, because of their large number compared to higher magnitude events, the characterization of small‐magnitude crustal earthquakes is key to identify active structures and better constrain the tectonic models. In this work, we exploit 53 months of continuously recorded, three‐component waveforms from the permanent seismic network in central Chile using a deep‐learning approach to improve the detection of small‐magnitude earthquakes. To increase station coverage, we also use the seismic phases obtained from a previous temporary seismic deployment. We use the obtained seismicity catalog to refine tomographic models of that region, revealing a more detailed architecture of the Chilean forearc. Travel times calculated in the new 3‐D velocity model allowed us to locate ∼14,000 earthquakes. Refined double‐difference relocations of ∼4,900 events located beneath the West Andean Thrust suggest a large‐scale, west‐dipping structure which, together with the west‐verging tectonic front, likely contributed to the uplift and crustal deformation during the past ∼20 Myr. Plain Language Summary: The occurrence of earthquakes is closely related to plate tectonics and in particular, the creation of mountain ranges and their evolution over very long periods of time. In order to better understand how these processes work in the Andes of Central Chile, we analyze more than 4 years of earthquake records using a machine learning algorithm. This technique allows us to automatically and reliably detect very small earthquakes, that are, in general, missing in the seismicity catalogs. Since they are also more numerous, we can use them to improve the geophysical images and reveal more details of crustal structures. We find that most of the superficial earthquakes beneath the Andean Cordillera are aligned with a major structure, dipping toward the west. This structure accommodates processes of shortening and uplifting directly related to the construction of the Andes. Key Points: A large number of earthquakes detected using a deep‐learning approach are used for local earthquake tomographyThe obtained 3‐D seismic wave velocity structure is used to relocate the seismicity catalogEarthquake locations suggest a west‐dipping major structure that we interpret to have contributed to the uplift of the South‐Central Andes [ABSTRACT FROM AUTHOR]

In this work we propose a detailed analysis of the crustal seismicity characterizing the Sierras de Córdoba (Eastern Sierras Pampeanas, central Argentina). We considered a large number of first P- and S-wave arrivals with good azimuthal coverage by the SIEMBRA and ESP temporary seismic networks along with a regionally calibrated velocity model. We obtained accurate hypocentral solutions and related them with possible faulting basement structures. Our results indicate that the crustal seismicity of the Sierras de Córdoba is mainly concentrated to the north, west and south-west of the Sierra Grande. In addition, the seismicity at depth seems to be preferentially distributed at middle crustal levels (depths ranging from 10 to 26 km). Focal mechanisms solutions obtained from P-wave first motion polarities and P–S amplitude ratios are predominantly reverse and could be associated with the extension at depth of the Sierra de Pocho, Sierra Grande and Ciénaga del Coro faults. The magnitudes are comprised between 1.6 ≤ M L ≤ 3.3 and 1.7 ≤ M W ≤ 3.4. They represent the first estimates for small-to-moderate sized earthquakes occurring in the Sierras de Córdoba and recorded by local, temporary seismological networks. • In plan, the earthquakes in the Sierras de Córdoba are heterogeneously distributed. • The middle crustal levels concentrate the highest number of earthquakes. • Focal mechanisms show the extension of the Sierra de Pocho fault at depth. • Sierra de Grande fault is recognized at depth from determined focal mechanisms. • Ciénaga del Coro fault is identified from focal mechanisms in the middle-crust. [ABSTRACT FROM AUTHOR]

In the central Andes, the Nazca plate displays large along strike variations in dip with a near horizontal subduction angle between 28 and 32°S referred to the Pampean flat slab segment. The upper plate above the Pampean flat slab has high rates of crustal seismicity and active basement cored uplifts. The SIEMBRA experiment, a 43-broad-band-seismic-station array was deployed to better characterize the Pampean flat slab region around 31°S. In this study, we explore the lithospheric structure above the flat slab as a whole and its relation to seismicity. We use the SIEMBRA data to perform a joint inversion of teleseismic receiver functions and Rayleigh wave phase velocity dispersion to constrain the shear wave velocity variations in the lithosphere. Our joint inversion results show: (1) the presence of several upper-plate mid-crustal discontinuities and their lateral extent that are probably related to the terrane accretion history; (2) zones of high shear wave velocity in the upper-plate lower crust associated with a weak Moho signal consistent with the hypothesis of partial eclogitization in the lower crust; (3) the presence of low shear-wave velocities at ~100 km depth interpreted as the subducting oceanic crust. Finally, in order to investigate the relation of the lithospheric structure to seismicity, we determine an optimal velocity-depth model based on the joint inversion results and use it to perform regional moment tensor inversions (SMTI) of crustal and slab earthquakes. The SMTI for 18 earthquakes that occurred between 2007 and 2009 in the flat slab region below Argentina, indicates systematically shallower focal depths for slab earthquakes (compared with inversions using previous velocity models). This suggests that the slab seismicity is concentrated mostly between 90 and 110 km depths within the subducting Nazca plate's oceanic crust and likely related to dehydration. In addition, the slab earthquakes exhibit extensional focal mechanisms suggesting new faulting at the edges of the flat portion of the slab. SMTI solutions for upper-plate crustal earthquakes match well the geological observations of reactivated structures and agree with crustal shortening. Our new constraints on flat slab structure can aid earthquake characterization for regional seismic hazard assessment and efforts to help understand the mechanisms for slab flattening in the central Andes. [ABSTRACT FROM AUTHOR]

The Magallanes-Fagnano fault (at ~51-56°S) is a continental NW-SE transform fault zone that marks the boundary between the South American Plate (north) and the Scotia Plate (South). In 1949, two crustal seismic events of estimated magnitude M > 7 were located in this area using teleseismic records. Although, this region is scarcely populated, such shallow seismicity could represent a considerable threat to the remote urban centers in this sector. The characterization of the local seismicity always lacked good quality records and permanent instrumentation. In the recent past years, permanent seismic stations (CSN and INPRES-CTBTO) were deployed in the Tierra del Fuego Island and Southern Patagonia, providing with continuous time, broadband records of waveform data. In order to obtain better insights about the local seismicity associated with the Magallanes-Fagnano fault, we jointly inverted teleseismic receiver functions with Rayleigh-wave dispersion data to build a calibrated velocity model for the study region. In parallel, we analyzed the continuous waveforms to automatically detect local earthquakes and locate them using our regional velocity model. Our results show: 1) Shallow seismic events distributed along the Magallanes-Fagnano fault. 2) Diffuse seismicity characterizing the South American crust, north of 53°S. Our observations suggest two mechanisms of crustal deformation. In the Tierra del Fuego Island the seismicity is mostly associated with the Magallanes-Fagnano fault system. In the Southern Patagonia, along the Patagonian Andes the seismicity would be mostly due to isostatic rebound following the retreat of the Patagonian Ice sheet. • A new regional velocity model for the Southern Patagonia and Tierra del Fuego. • New hypocenter locations from local seismicity records. • The Magallanes-Fagnano fault is the main mechanism of crustal deformation in Tierra del Fuego. • Isostatic rebound may be the main mechanism of crustal deformation in the Southern Andes. [ABSTRACT FROM AUTHOR]