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For several years, the interseismic period has been studied using geodetic data in different places worldwide, especially using coupling maps supposing constant deformation rates. The growing number of continuous global positioning system (GPS) stations and development of new detection techniques have facilitated the detection of a wide range of transient deformation, even masked in the noise. The GPS networks of the South Peru – North Chile subduction zone have seen an increase in continuous GPS stations over the past decade, which is a good opportunity to investigate the details of non-linear interseismic deformation in these areas. In this study, we apply a geodetic matched-filter approach (Rousset et al., 2017, JGR) in the residual time series of 66 GPS stations available in the region over 10 years. The method allows us to detect 41 potential small slow slip events (sSSEs), with magnitudes ranging from 6.1 to 6.9 and duration from 3 to 93 days. Most of these events are located at the deeper part of the seismogenic zone. The comparison of the detected sSSEs location with the interseismic coupling map shows that 68% of these events are located in areas of intermediate coupling, from 0.25 to 0.75. A comparison with the background seismicity in the region, reveals some interactions between sSSEs located in the transition zone and intermediate deep seismicity. This relationship between seismic and aseismic deformation might be related to processes associated with slab acceleration at depth prior to the occurrence of large earthquakes and/or postseismic deformation. [ABSTRACT FROM AUTHOR]

The Central Andes subduction has been the theater of numerous large earthquakes since the beginning of the 21st Century, notably the 2001 Mw = 8.4 Arequipa, 2007 Mw = 8.0 Pisco and 2014 Mw = 8.1 Iquique earthquakes. We present an analysis of 47 permanent and 26 survey global navigation satellite system (GNSS) measurements acquired in Central‐South Peru between 2007 and 2022 to better understand the frictional properties of the megathrust interface. Using a trajectory model that mimics the different phases of the cycle, we extract a coherent interseismic GNSS field at the scale of the Central Andes from Lima to Arica (12–18.5°S). Interseismic models on a 3D slab geometry indicate that the locking level is relatively high and concentrated between 20 and 40‐km depth. Locking distributions indicate a high spatial variability of the coupling along the trench, with the presence of many locked patches that spatially correlate with the seismotectonic segmentation. Our study confirms the presence of a creeping segment where the Nazca Ridge is subducting; we also observe a lighter apparent decrease of coupling related to the Nazca Fracture Zone (NFZ). However, since the Nazca Ridge appears to behave as a strong barrier, the NFZ is less efficient to arrest seismic rupture propagation. Considering various uncertainty factors, we discuss the implication of our coupling estimates with size and timing of large megathrust earthquakes considering both deterministic and probabilistic approaches. We estimate that the South Peru segment could have a Mw = 8.4–9.0 earthquake potential depending principally on the considered seismic catalog and the seismic/aseismic slip ratio. Plain Language Summary: Using dense global navigation satellite system (GNSS) data collected in the South‐Central Peru, we extracted a large scale interseismic velocity (surface velocity between two earthquakes) field at the scale of the Central Andes of Peru, where the oceanic Nazca plate goes under the continental South America plate at a velocity of about 6 cm/yr. This area has been the theater of several great subduction earthquakes and tsunamis, then estimating the stress build‐up on the subduction interface is key to better anticipate future large earthquakes. Through a modeling of the GNSS velocities on a 3D slab geometry, we were able to obtain useful informations on the location, size, magnitude and return period of future great earthquakes in South Peru. Thereby, we obtained a very heterogeneous spatial distribution of interseismic coupling (degree of locking between the two tectonic plates), with low‐coupled areas where the Nazca Ridge and the Nazca Fracture Zone are subducting, but highly‐coupled areas close to the coasts of Lima and Arequipa. Finally, we estimate that the South Peru segment between the Nazca Ridge and the Arica band could have the potential to host a Mw = 8.4 to Mw = 9.0 earthquake, with a one century and one millennial recurrence time respectively. Key Points: We present a dense interseismic velocity field at the scale of the South Peruvian Andes, from new decadal global navigation satellite system data at 73 locationsLow locking (∼0.4) is estimated along the Nazca Ridge and the Nazca Fracture Zone, delimiting wide patches of high locking (∼0.9)Moment budget analysis shows that the South Peru segment could host a Mw = 8.4–9.0 earthquake with a 100 to 1,000 years recurrence time [ABSTRACT FROM AUTHOR]

Abstract We study the rupture processes of Iquique earthquake M w 8.1 (2014/04/01) and its largest aftershock M w 7.7 (2014/04/03) that ruptured the North Chile subduction zone. High-rate Global Positioning System (GPS) recordings and strong motion data are used to reconstruct the evolution of the slip amplitude, rise time and rupture time of both earthquakes. A two-step inversion scheme is assumed, by first building prior models for both earthquakes from the inversion of the estimated static displacements and then, kinematic inversions in the frequency domain are carried out taken into account this prior information. The preferred model for the mainshock exhibits a seismic moment of 1.73 × 1021 Nm (M w 8.1) and maximum slip of ∼9 m, while the aftershock model has a seismic moment of 3.88 × 1020 (M w 7.7) and a maximum slip of ∼3 m. For both earthquakes, the final slip distributions show two asperities (a shallow one and a deep one) separated by an area with significant slip deficit. This suggests a segmentation along-dip which might be related to a change of the dipping angle of the subducting slab inferred from gravimetric data. Along-strike, the areas where the seismic ruptures stopped seem to be well correlated with geological features observed from geophysical information (high-resolution bathymetry, gravimetry and coupling maps) that are representative of the long-term segmentation of the subduction margin. Considering the spatially limited portions that were broken by these two earthquakes, our results support the idea that the seismic gap is not filled yet. Highlights • Causes of along-strike and -dip segmentations are revealed by Iquique earthquake. • This study shows that the Northern Chile seismic gap is not fully filled yet. • A multigrid two-step kinematic study is performed to avoid possible local minima. • Kinematic models are constrained by prior models built from static inversions. [ABSTRACT FROM AUTHOR]

Following laboratory experiments and friction theory, slow slip events and seismicity rate accelerations observed before mainshocks are sometimes interpreted as evidence of a nucleation phase. However, such precursory observations still remain scarce and are associated with different time and length scales, raising doubts about their actual preparatory nature. We study the 2017 Valparaiso Mw = 6.9 earthquake, which was preceded by aseismic slip accompanied by an intense seismicity, suspected to reflect its nucleation phase. We complement previous observations, which have focused only on precursory activity, with a continuous investigation of seismic and aseismic processes from the foreshock sequence to the post‐mainshock phase. By building a high‐resolution earthquake catalog and searching for anomalous seismicity rate increases compared to aftershock triggering models, we highlight an over‐productive seismicity starting within the foreshock sequence and persisting several days after the mainshock. Using repeating earthquakes and high‐rate GPS observations, we highlight a transient aseismic perturbation starting 1‐day before the first foreshock and continuing after the mainshock. The estimated slip rate over time is lightly impacted by large magnitude earthquakes and does not accelerate toward the mainshock. Therefore, the unusual seismic and aseismic activity observed during the 2017 Valparaiso sequence might be interpreted as the result of a slow slip event starting before the mainshock and continuing beyond it. Rather than pointing to a possible nucleation phase of the 2017 Valparaiso mainshock, the identified slow slip event acts as an aseismic loading of nearby faults, increasing the seismic activity, and thus the likelihood of a large rupture. Plain Language Summary: Both laboratory experiments and friction theory show that earthquakes do not begin abruptly but are preceded by an accelerating slip associated with a seismicity increase. On the field, however, such precursory observations still remain scarce and are associated with different characteristic time and length scales, raising doubts that they actually reflect the same nucleation phenomena. We study the 2017 Valparaiso M = 6.9 earthquake, which was preceded by both a slow slip and an intense seismicity suspected to reflect such nucleation phase. We complement previous studies, that have focused only on precursory activity, with a continuous investigation of seismic and slow slip before and after the mainshock. Using refined earthquake detection tools, we highlight a seismicity excess starting before and persisting several days after the mainshock. Using repeating earthquakes and high‐resolution GPS, we show that the slow slip does not accelerate toward the mainshock, but continues after it. Therefore, rather than pointing to a possible accelerating nucleation phase of the Valparaiso mainshock, we suggest that the slow slip drives an enhanced seismic activity that is not mainshock‐directed. Within such slow‐slip driven seismicity, the probability of triggering a large earthquake (subsequently considered as the mainshock) is increased. Key Points: We use a high resolution seismic catalog and GPS to investigate seismic and aseismic process before and after the Valparaiso mainshockAn unusually high seismicity and a slow slip event is continuously observed from the foreshock sequence up to days after the mainshockRather than a nucleation phase of the mainshock, the slow slip event acts as an aseismic loading of nearby faults during the entire sequence [ABSTRACT FROM AUTHOR]

Abstract: Slow slip events (SSEs) regularly occur near the Boso Peninsula, central Japan. Their time of recurrence has been decreasing from 6.4 to 2.2 years from 1996 to 2014. It is important to better constrain the slip history of this area, especially as models show that the recurrence intervals could become shorter prior to the occurrence of a large interplate earthquake nearby. We analyze the seismic waveforms of more than 2,900 events (M≥1.0) taking place in the Boso Peninsula, Japan, from 1 April 2004 to 4 November 2015, calculating the correlation and the coherence between each pair of events in order to define groups of repeating earthquakes. The cumulative number of repeating earthquakes suggests the existence of two slow slip events that have escaped detection so far. Small transient displacements observed in the time series of nearby GPS stations confirm these results. The detection scheme coupling repeating earthquakes and GPS analysis allow to detect small SSEs that were not seen before by classical methods. This work brings new information on the diversity of SSEs and demonstrates that the SSEs in Boso area present a more complex history than previously considered. [ABSTRACT FROM AUTHOR]