Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at t... more Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at the global scale. However, no such event has been described in the south Peru - north Chile subduction zone so far, except for the early preparatory phase of the 2014 Iquique earthquake. We use geodetic template matching on GNSS-derived time series of surface motion in Northern Chile to extract SSEs hidden within the geodetic noise. We detect 33 events with durations ranging from 9 to 40 days and magnitudes from $M_w$~5.6 to 6.2. The moment released by these aseismic events seems to scale with the cube of their duration, suggesting a dynamic comparable to that of earthquakes. We compare the distribution of SSEs with the distribution of coupling along the megathrust derived using Bayesian inference on GNSS- and InSAR-derived interseismic velocities. From this comparison, we obtain that most SSEs occur in regions of intermediate coupling where the megathrust transitions from locked to creep...
Estimates of the onset times of P phases from active source experiments can effectively be used i... more Estimates of the onset times of P phases from active source experiments can effectively be used in developing wavespeed models, and the large number of recordings typical of such experiments incentivizes the development of automated approaches to generate these estimates. The simplicity and repeatability of an airgun source such as that used in the 2016 Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source (PICTURES) project in northern Chile suggested that a straightforward application of waveform cross-correlation would suffice for arrivals recorded by a network of inland seismic stations, but did not work well due to significant variations in waveform morphology. Application of an alternative algorithm typically used in passive source investigations, the Regressive ESTimator (REST) autopicking package, also proved unsatisfactory, largely because the limited spectral bandwidth of the airgun source and the frequent occurrence of local seismicity led t...
The M8.1 2014 Iquique earthquake broke a central piece of the long-standing, >500 km long nort... more The M8.1 2014 Iquique earthquake broke a central piece of the long-standing, >500 km long northern Chile seismic gap. The Iquique earthquake sequence started off with a M6.7 thrust event presumably in the upper plate seaward of the Chilean coastline. Deformation was quickly transferred onto the megathrust with three more events of M>6 until it culminated in the mainshock that broke a compact asperity with possibly up to 12 m of slip two weeks later. The mainshock was followed by vigorous aftershock sequence, including a M7.7 event just south of the main slip patch approx. two days later.
The Civil Engineering Department of the University of Chile, together with international institut... more The Civil Engineering Department of the University of Chile, together with international institutions deployed strong motion stations in the northern Chile seismic gap. These networks recorded the June 23, 2001 Mw=8.4 earthquake that occurred in Southern Peru, which is the strongest event in the last 25 years. This earthquake exhibited, at stiff soil sites, in northern Chile relatively large maximum velocities and accelerations although the recording stations are located more than 400 km away from the epicentral region and 200 km from the southern edge of the rupture. Damage to infrastructure was observed in adobe housing and low strength structures. Typical accelerations are in the order of 0.30 g, considerably larger than those expected from typical attenuation formulas if epicentral distances are considered.
Journal of Geophysical Research: Solid Earth, 2019
We used data from >100 permanent and temporary seismic stations to investigate seismicity patt... more We used data from >100 permanent and temporary seismic stations to investigate seismicity patterns related to the 1 April 2014 M8.1 Iquique earthquake in northern Chile. Applying a multistage automatic event location procedure to the seismic data, we detected and located ~19,000 foreshocks, aftershocks, and background seismicity for 1 month preceding and 9 months following the mainshock. Foreshocks skirt around the updip limit of the mainshock asperity; aftershocks occur mainly in two belts updip and downdip of it. The updip seismicity primarily locates in a zone of transitional friction on the megathrust and can be explained by preseismic stress loading due to slow‐slip processes and afterslip driven by increased Coulomb failure stress due to the mainshock and its largest aftershock. Afterslip further south also triggered aftershocks and repeating earthquakes in several EW striking streaks. We interpret the streaks as markers of surrounding creep that could indicate a change in fault mechanics and may have structural origin, caused by fluid‐induced failure along presumed megathrust corrugations. Megathrust aftershocks terminate updip below the seaward frontal prism in the outer continental wedge that probably behaves aseismically under velocity‐strengthening conditions. The inner wedge locates further landward overlying the megathrust's seismogenic zone. Further downdip, aftershocks anticorrelate with the two major afterslip patches resolved geodetically and partially correlate with increased Coulomb failure stress, overall indicating heterogeneous frictional behavior. A region of sparse seismicity at ~40‐ to 50‐km depth is followed by the deepest plate interface aftershocks at ~55‐ to 65‐km depth, which occur in two clusters of significantly different dip.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In this work, new strategies for automatic identification of P-and S-wave arrival times from digi... more In this work, new strategies for automatic identification of P-and S-wave arrival times from digital recorded local seismograms are proposed and analyzed. The database of arrival times previously identified by a human reader was compared with automatic identification techniques based on the Fourier transformation in reduced time (spectrograms), fractal analysis, and the basic matching pursuit algorithm. The first two techniques were used to identify the Pwave arrival times, while the third was used for the identification of the S-wave. For validation, the results were compared with the short-time average over longtime average (STA/LTA) of Rietbrock et al., Geophys Res Lett 39(8), (2012) for the database of aftershocks of the 2010 Maule M w = 8.8 earthquake. The identifiers proposed in this work exhibit good results that outperform the STA/LTA identifier in many scenarios. The average difference from the reference picks
The magnitude 7.7 Tocopilla earthquake of November 14, 2007 ruptured a stretch of the northern Ch... more The magnitude 7.7 Tocopilla earthquake of November 14, 2007 ruptured a stretch of the northern Chile subduction zone just north of the 1995 Antofagasta earthquake source region. In this study, we compare a Bayesian analysis with a simulated annealing inversion methodology to determine a finite fault rupture model for the Tocopilla earthquake. While we also incorporate both teleseismic data and satellite radar images, high-rate (5 samples/sec) GPS data provides particularly important constraints on the source process of this event. Because the Tocopilla earthquake was located immediately coastward of the CANTO (Central ANdean Tectonic Observatory) geodetic network, the evolution of the local slip field is well-recorded. We find that the high-rate continuous GPS data is key to determining the location of the hypocenter and asperities as well as the evolution of slip. Most of the slip is located east of the coastline with at least two distinct regions of concentrated slip.
Understanding the processes behind subduction-related hazards is an important responsibility and ... more Understanding the processes behind subduction-related hazards is an important responsibility and major challenge for Earth scientists. Few areas demonstrate this as clearly as south-central Chile, where the largest instrumentally-recorded earthquake occurred (the 1960 Mw 9.5 Valdivia earthquake) in the same region as one of South America's most active volcanoes, Villarrica. The geometry and geophysical characteristics of the subduction system are well constrained north of 39°S, but not further south where the 1960 coseismic slip was greatest. This region has long been considered a seismic gap due to the scarcity of local earthquakes registered in this region both by international networks (IRIS-NEIC) and the Chilean National Seismological Service (SSN). In the framework of the collaborative research centre SFB 574, the south-central Chilean subduction zone is investigated by a seismological subproject conducted by Chilean, Argentinian and German partners. This study presents re...
Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at t... more Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at the global scale. However, no such event has been described in the south Peru - north Chile subduction zone so far, except for the early preparatory phase of the 2014 Iquique earthquake. We use geodetic template matching on GNSS-derived time series of surface motion in Northern Chile to extract SSEs hidden within the geodetic noise. We detect 33 events with durations ranging from 9 to 40 days and magnitudes from $M_w$~5.6 to 6.2. The moment released by these aseismic events seems to scale with the cube of their duration, suggesting a dynamic comparable to that of earthquakes. We compare the distribution of SSEs with the distribution of coupling along the megathrust derived using Bayesian inference on GNSS- and InSAR-derived interseismic velocities. From this comparison, we obtain that most SSEs occur in regions of intermediate coupling where the megathrust transitions from locked to creep...
Estimates of the onset times of P phases from active source experiments can effectively be used i... more Estimates of the onset times of P phases from active source experiments can effectively be used in developing wavespeed models, and the large number of recordings typical of such experiments incentivizes the development of automated approaches to generate these estimates. The simplicity and repeatability of an airgun source such as that used in the 2016 Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source (PICTURES) project in northern Chile suggested that a straightforward application of waveform cross-correlation would suffice for arrivals recorded by a network of inland seismic stations, but did not work well due to significant variations in waveform morphology. Application of an alternative algorithm typically used in passive source investigations, the Regressive ESTimator (REST) autopicking package, also proved unsatisfactory, largely because the limited spectral bandwidth of the airgun source and the frequent occurrence of local seismicity led t...
The M8.1 2014 Iquique earthquake broke a central piece of the long-standing, >500 km long nort... more The M8.1 2014 Iquique earthquake broke a central piece of the long-standing, >500 km long northern Chile seismic gap. The Iquique earthquake sequence started off with a M6.7 thrust event presumably in the upper plate seaward of the Chilean coastline. Deformation was quickly transferred onto the megathrust with three more events of M>6 until it culminated in the mainshock that broke a compact asperity with possibly up to 12 m of slip two weeks later. The mainshock was followed by vigorous aftershock sequence, including a M7.7 event just south of the main slip patch approx. two days later.
The Civil Engineering Department of the University of Chile, together with international institut... more The Civil Engineering Department of the University of Chile, together with international institutions deployed strong motion stations in the northern Chile seismic gap. These networks recorded the June 23, 2001 Mw=8.4 earthquake that occurred in Southern Peru, which is the strongest event in the last 25 years. This earthquake exhibited, at stiff soil sites, in northern Chile relatively large maximum velocities and accelerations although the recording stations are located more than 400 km away from the epicentral region and 200 km from the southern edge of the rupture. Damage to infrastructure was observed in adobe housing and low strength structures. Typical accelerations are in the order of 0.30 g, considerably larger than those expected from typical attenuation formulas if epicentral distances are considered.
Journal of Geophysical Research: Solid Earth, 2019
We used data from >100 permanent and temporary seismic stations to investigate seismicity patt... more We used data from >100 permanent and temporary seismic stations to investigate seismicity patterns related to the 1 April 2014 M8.1 Iquique earthquake in northern Chile. Applying a multistage automatic event location procedure to the seismic data, we detected and located ~19,000 foreshocks, aftershocks, and background seismicity for 1 month preceding and 9 months following the mainshock. Foreshocks skirt around the updip limit of the mainshock asperity; aftershocks occur mainly in two belts updip and downdip of it. The updip seismicity primarily locates in a zone of transitional friction on the megathrust and can be explained by preseismic stress loading due to slow‐slip processes and afterslip driven by increased Coulomb failure stress due to the mainshock and its largest aftershock. Afterslip further south also triggered aftershocks and repeating earthquakes in several EW striking streaks. We interpret the streaks as markers of surrounding creep that could indicate a change in fault mechanics and may have structural origin, caused by fluid‐induced failure along presumed megathrust corrugations. Megathrust aftershocks terminate updip below the seaward frontal prism in the outer continental wedge that probably behaves aseismically under velocity‐strengthening conditions. The inner wedge locates further landward overlying the megathrust's seismogenic zone. Further downdip, aftershocks anticorrelate with the two major afterslip patches resolved geodetically and partially correlate with increased Coulomb failure stress, overall indicating heterogeneous frictional behavior. A region of sparse seismicity at ~40‐ to 50‐km depth is followed by the deepest plate interface aftershocks at ~55‐ to 65‐km depth, which occur in two clusters of significantly different dip.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In this work, new strategies for automatic identification of P-and S-wave arrival times from digi... more In this work, new strategies for automatic identification of P-and S-wave arrival times from digital recorded local seismograms are proposed and analyzed. The database of arrival times previously identified by a human reader was compared with automatic identification techniques based on the Fourier transformation in reduced time (spectrograms), fractal analysis, and the basic matching pursuit algorithm. The first two techniques were used to identify the Pwave arrival times, while the third was used for the identification of the S-wave. For validation, the results were compared with the short-time average over longtime average (STA/LTA) of Rietbrock et al., Geophys Res Lett 39(8), (2012) for the database of aftershocks of the 2010 Maule M w = 8.8 earthquake. The identifiers proposed in this work exhibit good results that outperform the STA/LTA identifier in many scenarios. The average difference from the reference picks
The magnitude 7.7 Tocopilla earthquake of November 14, 2007 ruptured a stretch of the northern Ch... more The magnitude 7.7 Tocopilla earthquake of November 14, 2007 ruptured a stretch of the northern Chile subduction zone just north of the 1995 Antofagasta earthquake source region. In this study, we compare a Bayesian analysis with a simulated annealing inversion methodology to determine a finite fault rupture model for the Tocopilla earthquake. While we also incorporate both teleseismic data and satellite radar images, high-rate (5 samples/sec) GPS data provides particularly important constraints on the source process of this event. Because the Tocopilla earthquake was located immediately coastward of the CANTO (Central ANdean Tectonic Observatory) geodetic network, the evolution of the local slip field is well-recorded. We find that the high-rate continuous GPS data is key to determining the location of the hypocenter and asperities as well as the evolution of slip. Most of the slip is located east of the coastline with at least two distinct regions of concentrated slip.
Understanding the processes behind subduction-related hazards is an important responsibility and ... more Understanding the processes behind subduction-related hazards is an important responsibility and major challenge for Earth scientists. Few areas demonstrate this as clearly as south-central Chile, where the largest instrumentally-recorded earthquake occurred (the 1960 Mw 9.5 Valdivia earthquake) in the same region as one of South America's most active volcanoes, Villarrica. The geometry and geophysical characteristics of the subduction system are well constrained north of 39°S, but not further south where the 1960 coseismic slip was greatest. This region has long been considered a seismic gap due to the scarcity of local earthquakes registered in this region both by international networks (IRIS-NEIC) and the Chilean National Seismological Service (SSN). In the framework of the collaborative research centre SFB 574, the south-central Chilean subduction zone is investigated by a seismological subproject conducted by Chilean, Argentinian and German partners. This study presents re...
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