German A. A Prieto | Universidad Nacional de Colombia (National University of Colombia) (original) (raw)

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Papers by German A. A Prieto

Geophysical Research Letters, 2013

Intermediate‐depth earthquakes occur at depths where temperatures and pressures exceed those at w... more Intermediate‐depth earthquakes occur at depths where temperatures and pressures exceed those at which brittle failure is expected. There are two leading candidates for the physical mechanism behind these earthquakes: dehydration embrittlement and self‐localizing thermal shear runaway. A complete energy budget for a range of earthquake sizes can help constrain whether either of these mechanisms might play a role in intermediate‐depth earthquake rupture. The combination of high stress drop and low radiation efficiency that we observe for Mw 4–5 earthquakes in the Bucaramanga Nest implies a temperature increase of 600–1000°C for a centimeter‐scale layer during earthquake failure. This suggests that substantial shear heating, and possibly partial melting, occurs during intermediate‐depth earthquake failure. Our observations support thermal shear runaway as the mechanism for intermediate‐depth earthquakes, which would help explain differences in their behavior compared to shallow earthqu...

Bulletin of the Seismological Society of America, 2017

Journal of Geophysical Research: Solid Earth, 2017

Mechanical Systems and Signal Processing, 2017

Science Advances, 2016

Researchers monitor southwest Greenland’s ice sheet mass changes by measuring seismic velocity va... more Researchers monitor southwest Greenland’s ice sheet mass changes by measuring seismic velocity variations in Greenland’s crust.

Geophysical Research Letters, 2016

Geochemistry, Geophysics, Geosystems, 2016

Journal of Geophysical Research: Solid Earth, 2013

Science, 2014

Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismi... more Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismic waves. Simulations of seismic wave propagation in sedimentary basins capture this effect; however, there exists no method to validate these results for earthquakes that have not yet occurred. We present a new approach for ground motion prediction that uses the ambient seismic field. We apply our method to a suite of magnitude 7 scenario earthquakes on the southern San Andreas fault and compare our ground motion predictions with simulations. Both methods find strong amplification and coupling of source and structure effects, but they predict substantially different shaking patterns across the Los Angeles Basin. The virtual earthquake approach provides a new approach for predicting long-period strong ground motion.

Geophysical Journal International, 2011

Comptes Rendus Geoscience, 2011

Bulletin of the Seismological Society of America, 2010

Geosphere

The recycling of water into the Earth’s mantle via hydrated oceanic lithosphere is believed to ha... more The recycling of water into the Earth’s mantle via hydrated oceanic lithosphere is believed to have an important role in subduction zone seismicity at intermediate depths. Hydration of oceanic lithosphere has been shown to drive double planes of intermediate-depth, Wadati-Benioff zone seismicity at subduction zones. However, observations from trenches show that pervasive normal faulting causes hydration ~25 km into the lithosphere and can explain neither locations where separations of 25–40 km between Wadati-Benioff zone planes are observed nor the spatial variability of the lower plane in these locations, which suggests that an additional mechanism of hydration exists. We suggest that intraplate deformation of >50-m.y.-old lithosphere, an uncommon and localized process, drives deeper hydration. To test this, we relocated the 25 November 2018 6.0 MW Providencia, Colombia, earthquake mainshock and 575 associated fore- and aftershocks within the interior of the Caribbean oceanic pl...

Earth and Planetary Science Letters, 2022

Both the Caribbean and Nazca plates subduct beneath northwestern South America. The configuration... more Both the Caribbean and Nazca plates subduct beneath northwestern South America. The configuration of the two subducted slabs and the nature of any interaction between them has long been a matter of debate. Based on the location of intermediate-depth seismicity and active and extinct volcanism, as well as on seismic imaging, several different tectonic scenarios have been proposed. In this paper, we use teleseismic data recorded by the Colombian National Network and the temporary CARMA array in Venezuela and Colombia to produce a finite-frequency tomography model for the region. Our results show several distinct subduction segments. Through synthetic tests, we show that our results require a zone of overlap between Nazca and Caribbean subduction north of the "Caldas Tear" as has been proposed by previous studies. Additionally, we find that the Bucaramanga Nest occurs within the Caribbean Plate and coincides with bending of the slab in two planes, where both the strike and the dip of the slab change. We infer that elevated stresses are an important factor in producing the very high rates of seismicity in the nest.

Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containi... more Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containing the puzzling seismic feature known as the Bucaramanga nest. We relocate about 5000 earthquakes recorded by the Colombian national seismic network and produce the first 3-D velocity model of the area to define the geometry of the lithosphere subducting below the Colombian Andes. We found lateral velocity heterogeneities and an abrupt offset of the Wadati-Benioff zone at 58N indicating that the Nazca plate is segmented by an E-W slab tear, that separates a steeper Nazca segment to the south from a flat subduction to the north. The flat Nazca slab extends eastward for about 400 km, before dip increases to 508 beneath the Eastern Cordillera, where it yields the Bucaramanga nest. We explain this puzzling locus of intermediate-depth seismicity located beneath the Eastern Cordillera of Colombia as due to a massive dehydration and eclogitization of a thickened oceanic crust. We relate the flat subducting geometry to the entrance at the trench at ca. 10 Ma of a thick-buoyant oceanic crust, likely a volcanic ridge, producing a high coupling with the overriding plate. Sub-horizontal plate subduction is consistent with the abrupt disappearance of volcanism in the Andes of South America at latitudes > 58N.

The systematic behavior of earthquake rupture as a function of earthquake magnitude and/or tecton... more The systematic behavior of earthquake rupture as a function of earthquake magnitude and/or tectonic setting is a key in our understanding of the physical mechanisms involved during earthquake rupture. Geophysical evidence suggests that although deep earthquakes—including intermediate-depth and deep—are similar to shallow ones, the mechanism involved during deep earthquakes is different from that of shallow ones. In particular, the magnitude and depth dependence of scaled duration, a measure of earthquake rupture duration, has led to controversy of what controls deep earthquake behavior. Here we estimate scaled source durations for 600 intermediate-depth and deep-focus earthquakes recorded at teleseismic distances and show deviation from self-similar scaling. No depth dependence is observed which we interpret as due to little differences between intermediate-depth and deep-focus earthquake mechanisms. The data show no correlation between durations and plate age or thermal parameters, suggesting that the thermal properties of the plate have little effect on source durations. We nevertheless report differences in average source duration and scaling between subduction zones and along-strike variations of source durations that more closely resemble the geometry of subduction (flat or steep subduction) rather than plate age.

Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismi... more Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying
seismic waves. Simulations of seismic wave propagation in sedimentary basins capture
this effect; however, there exists no method to validate these results for earthquakes that
have not yet occurred. We present a new approach for ground motion prediction that
uses the ambient seismic field. We apply our method to a suite of magnitude 7 scenario
earthquakes on the southern San Andreas fault and compare our ground motion predictions
with simulations. Both methods find strong amplification and coupling of source and structure
effects, but they predict substantially different shaking patterns across the Los Angeles Basin.
The virtual earthquake approach provides a new approach for predicting long-period strong
ground motion.

We investigate the global rupture parameters for deep and intermediate-depth earthquakes. From me... more We investigate the global rupture parameters for deep and intermediate-depth earthquakes. From measurements of rupture duration and radiated seismic energy we estimate stress drop, apparent stress, and radiation efficiency and obtain a detailed earthquake energy budget. From scaling of the source parameters we highlight differences between crustal and deep seismicity, with the latter showing larger fracture energies. The observed increase of radiation efficiency with depth suggests that rupture mechanism for deep and intermediate-depth events differs. In agreement with previous studies we observe along-strike variability of rupture properties for deep and intermediate-depth earthquakes, correlating with slab morphology, plate age, or presence of volcanic structures.

Sound speed inversions made using simulated time of flight data from a numerical limb-mimicking p... more Sound speed inversions made using simulated time of flight data from a numerical limb-mimicking phantom comprised of soft tissue and a bone inclusion demonstrate that wave front tracking forward modeling combined with í µí°¿ 1 regularization could lead to accurate estimates of bone sound-speed. Ultrasonic tomographic imaging of limbs has the potential to impact prosthetic socket fitting, as well as detect and track muscular dystrophy diseases, osteoporosis and bone fractures at low cost and without radiation exposure. Research in ultrasound tomography of bones has increased in the last 10 years, however, methods delivering clinically useful sound-speed inversions are lacking. Inversions for the sound-speed of the numerical phantoms using í µí°¿ 1 and í µí°¿ 2 regularizations are compared using wave front forward models. The simulations are based on a custom-made cylindrically-scanning tomographic medical ultrasound system (0.5 – 5 MHz) consisting of two acoustic transducers capable of collecting pulse echo and travel time measurements over the entire 360° aperture.

Geophysical Research Letters, 2013

Intermediate‐depth earthquakes occur at depths where temperatures and pressures exceed those at w... more Intermediate‐depth earthquakes occur at depths where temperatures and pressures exceed those at which brittle failure is expected. There are two leading candidates for the physical mechanism behind these earthquakes: dehydration embrittlement and self‐localizing thermal shear runaway. A complete energy budget for a range of earthquake sizes can help constrain whether either of these mechanisms might play a role in intermediate‐depth earthquake rupture. The combination of high stress drop and low radiation efficiency that we observe for Mw 4–5 earthquakes in the Bucaramanga Nest implies a temperature increase of 600–1000°C for a centimeter‐scale layer during earthquake failure. This suggests that substantial shear heating, and possibly partial melting, occurs during intermediate‐depth earthquake failure. Our observations support thermal shear runaway as the mechanism for intermediate‐depth earthquakes, which would help explain differences in their behavior compared to shallow earthqu...

Bulletin of the Seismological Society of America, 2017

Journal of Geophysical Research: Solid Earth, 2017

Mechanical Systems and Signal Processing, 2017

Science Advances, 2016

Researchers monitor southwest Greenland’s ice sheet mass changes by measuring seismic velocity va... more Researchers monitor southwest Greenland’s ice sheet mass changes by measuring seismic velocity variations in Greenland’s crust.

Geophysical Research Letters, 2016

Geochemistry, Geophysics, Geosystems, 2016

Journal of Geophysical Research: Solid Earth, 2013

Science, 2014

Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismi... more Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismic waves. Simulations of seismic wave propagation in sedimentary basins capture this effect; however, there exists no method to validate these results for earthquakes that have not yet occurred. We present a new approach for ground motion prediction that uses the ambient seismic field. We apply our method to a suite of magnitude 7 scenario earthquakes on the southern San Andreas fault and compare our ground motion predictions with simulations. Both methods find strong amplification and coupling of source and structure effects, but they predict substantially different shaking patterns across the Los Angeles Basin. The virtual earthquake approach provides a new approach for predicting long-period strong ground motion.

Geophysical Journal International, 2011

Comptes Rendus Geoscience, 2011

Bulletin of the Seismological Society of America, 2010

Geosphere

The recycling of water into the Earth’s mantle via hydrated oceanic lithosphere is believed to ha... more The recycling of water into the Earth’s mantle via hydrated oceanic lithosphere is believed to have an important role in subduction zone seismicity at intermediate depths. Hydration of oceanic lithosphere has been shown to drive double planes of intermediate-depth, Wadati-Benioff zone seismicity at subduction zones. However, observations from trenches show that pervasive normal faulting causes hydration ~25 km into the lithosphere and can explain neither locations where separations of 25–40 km between Wadati-Benioff zone planes are observed nor the spatial variability of the lower plane in these locations, which suggests that an additional mechanism of hydration exists. We suggest that intraplate deformation of >50-m.y.-old lithosphere, an uncommon and localized process, drives deeper hydration. To test this, we relocated the 25 November 2018 6.0 MW Providencia, Colombia, earthquake mainshock and 575 associated fore- and aftershocks within the interior of the Caribbean oceanic pl...

Earth and Planetary Science Letters, 2022

Both the Caribbean and Nazca plates subduct beneath northwestern South America. The configuration... more Both the Caribbean and Nazca plates subduct beneath northwestern South America. The configuration of the two subducted slabs and the nature of any interaction between them has long been a matter of debate. Based on the location of intermediate-depth seismicity and active and extinct volcanism, as well as on seismic imaging, several different tectonic scenarios have been proposed. In this paper, we use teleseismic data recorded by the Colombian National Network and the temporary CARMA array in Venezuela and Colombia to produce a finite-frequency tomography model for the region. Our results show several distinct subduction segments. Through synthetic tests, we show that our results require a zone of overlap between Nazca and Caribbean subduction north of the "Caldas Tear" as has been proposed by previous studies. Additionally, we find that the Bucaramanga Nest occurs within the Caribbean Plate and coincides with bending of the slab in two planes, where both the strike and the dip of the slab change. We infer that elevated stresses are an important factor in producing the very high rates of seismicity in the nest.

Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containi... more Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containing the puzzling seismic feature known as the Bucaramanga nest. We relocate about 5000 earthquakes recorded by the Colombian national seismic network and produce the first 3-D velocity model of the area to define the geometry of the lithosphere subducting below the Colombian Andes. We found lateral velocity heterogeneities and an abrupt offset of the Wadati-Benioff zone at 58N indicating that the Nazca plate is segmented by an E-W slab tear, that separates a steeper Nazca segment to the south from a flat subduction to the north. The flat Nazca slab extends eastward for about 400 km, before dip increases to 508 beneath the Eastern Cordillera, where it yields the Bucaramanga nest. We explain this puzzling locus of intermediate-depth seismicity located beneath the Eastern Cordillera of Colombia as due to a massive dehydration and eclogitization of a thickened oceanic crust. We relate the flat subducting geometry to the entrance at the trench at ca. 10 Ma of a thick-buoyant oceanic crust, likely a volcanic ridge, producing a high coupling with the overriding plate. Sub-horizontal plate subduction is consistent with the abrupt disappearance of volcanism in the Andes of South America at latitudes > 58N.

The systematic behavior of earthquake rupture as a function of earthquake magnitude and/or tecton... more The systematic behavior of earthquake rupture as a function of earthquake magnitude and/or tectonic setting is a key in our understanding of the physical mechanisms involved during earthquake rupture. Geophysical evidence suggests that although deep earthquakes—including intermediate-depth and deep—are similar to shallow ones, the mechanism involved during deep earthquakes is different from that of shallow ones. In particular, the magnitude and depth dependence of scaled duration, a measure of earthquake rupture duration, has led to controversy of what controls deep earthquake behavior. Here we estimate scaled source durations for 600 intermediate-depth and deep-focus earthquakes recorded at teleseismic distances and show deviation from self-similar scaling. No depth dependence is observed which we interpret as due to little differences between intermediate-depth and deep-focus earthquake mechanisms. The data show no correlation between durations and plate age or thermal parameters, suggesting that the thermal properties of the plate have little effect on source durations. We nevertheless report differences in average source duration and scaling between subduction zones and along-strike variations of source durations that more closely resemble the geometry of subduction (flat or steep subduction) rather than plate age.

Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismi... more Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying
seismic waves. Simulations of seismic wave propagation in sedimentary basins capture
this effect; however, there exists no method to validate these results for earthquakes that
have not yet occurred. We present a new approach for ground motion prediction that
uses the ambient seismic field. We apply our method to a suite of magnitude 7 scenario
earthquakes on the southern San Andreas fault and compare our ground motion predictions
with simulations. Both methods find strong amplification and coupling of source and structure
effects, but they predict substantially different shaking patterns across the Los Angeles Basin.
The virtual earthquake approach provides a new approach for predicting long-period strong
ground motion.

We investigate the global rupture parameters for deep and intermediate-depth earthquakes. From me... more We investigate the global rupture parameters for deep and intermediate-depth earthquakes. From measurements of rupture duration and radiated seismic energy we estimate stress drop, apparent stress, and radiation efficiency and obtain a detailed earthquake energy budget. From scaling of the source parameters we highlight differences between crustal and deep seismicity, with the latter showing larger fracture energies. The observed increase of radiation efficiency with depth suggests that rupture mechanism for deep and intermediate-depth events differs. In agreement with previous studies we observe along-strike variability of rupture properties for deep and intermediate-depth earthquakes, correlating with slab morphology, plate age, or presence of volcanic structures.

Sound speed inversions made using simulated time of flight data from a numerical limb-mimicking p... more Sound speed inversions made using simulated time of flight data from a numerical limb-mimicking phantom comprised of soft tissue and a bone inclusion demonstrate that wave front tracking forward modeling combined with í µí°¿ 1 regularization could lead to accurate estimates of bone sound-speed. Ultrasonic tomographic imaging of limbs has the potential to impact prosthetic socket fitting, as well as detect and track muscular dystrophy diseases, osteoporosis and bone fractures at low cost and without radiation exposure. Research in ultrasound tomography of bones has increased in the last 10 years, however, methods delivering clinically useful sound-speed inversions are lacking. Inversions for the sound-speed of the numerical phantoms using í µí°¿ 1 and í µí°¿ 2 regularizations are compared using wave front forward models. The simulations are based on a custom-made cylindrically-scanning tomographic medical ultrasound system (0.5 – 5 MHz) consisting of two acoustic transducers capable of collecting pulse echo and travel time measurements over the entire 360° aperture.

A complete microseismic event catalog with accurate source parameters can lead to a more thorough... more A complete microseismic event catalog with accurate source parameters can lead to a more thorough understanding of the temporal and spatial variation of stress during hydraulic fracturing operations. We detect, locate, and characterize repeating microseismic events by determining their source parameters such as magnitude, stress drop, and rupture size, and analyze the continuous microseismic data recorded by one borehole array during a hydraulic injection process. With an existing microseismic event catalog, we first recalculate accurate moment magnitude and stress drop using estimated source spectra for all events. In addition, we detect and locate smaller events that show only clear S-wave arrivals using a template-matching and waveform cross-correlation technique to identify repeating microseismic activities. We obtain the template waveforms by stacking similar waveforms from repeating microseismic families. Among the ~1300 re-computed events, the moment magnitude calculated from the P-and S-waves spectra analysis ranges between Mw −1.5 and −3.5. These events are located within a 700m by 200m area as much as 250m deep. Our results indicate a fault radius on the order of one to six meters and fault slip between 10 −5 to 10 −3 cm around the fracturing region. In addition, using a matching-filter technique, we detect and locate low signal-to-noise ratio events that we consider repeating microseismic events. Our observations indicate that most repeating families occur at later times in shallower layers. Also, we observe a strong magnitude dependence of the stress drop, with larger magnitude events exhibiting significantly greater stress drops than smaller ones, in contrast to tectonic events in California or Japan. Our estimations of source parameters provide a key to a more in-depth understanding of the relationship between hydraulic fracturing and microseismic activity.