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Postseismic deformation following subduction earthquakes includes the combined effects of afterslip surrounding the coseismic rupture areas and viscoelastic relaxation in the asthenosphere and provides unique and valuable information for understanding the rheological structure. Because the two postseismic mechanisms are usually spatiotemporally intertwined, we developed an integrated model combining their contributions, based on 5 years of observations following the 2016 Pedernales (Ecuador) earthquake. The results show that the early, near‐field postseismic deformation is dominated by afterslip, both updip and downdip of the coseismic rupture, and requires heterogeneous interface frictional properties. Viscoelastic relaxation contributes more to far‐field displacements at later time periods. The best‐fit integrated model favors a 45‐km thick lithosphere overlying a Burgers body viscoelastic asthenosphere with a Maxwell viscosity of 3 × 1019 Pa s (0.9–5 × 1019 Pa s at 95% confidence), assuming the Kelvin viscosity equal to 10% of that value. In addition to the postseismic afterslip, the coastal displacement of sites north and south of the rupture clearly require extra slip in the plate motion direction due to slow slip events that may be triggered by the coseismic stress changes (CSC) but are not purely driven by the CSC. Spatially variable afterslip following the Pedernales event, combined with the SSEs during the interseismic period, demonstrate that spatial frictional variability persists throughout the whole earthquake cycle. The interaction of adjacent fault patches with heterogeneous properties may contribute to the clustered large earthquakes in this area. Plain Language Summary: On 16 April 2016 the Mw 7.8 Pedernales (Ecuador) earthquake struck the Nazca—South America subduction zone, which is one of the world's most important seismic belts. Earth movements after this earthquake were clearly recorded by nearby continuous Global Positioning System (CGPS) sites. The observed postseismic motions result from two main time‐dependent processes that responded to the earthquake: flow in the upper mantle (viscoelastic relaxation), and continuing slip on the fault plane surrounding the earthquake rupture (afterslip). We build a model to separate the contributions due to afterslip and viscoelastic relaxation from the CGPS time series 5 years after the Pedernales event. The results show that the early, near‐field postseismic deformation is mainly caused by afterslip, but viscoelastic relaxation contributes more to the far‐field observations, and is the largest signal in the later time period. We further discuss the implications of our modeling for providing a deeper understanding of the of the subduction zone earthquake cycle and the rheological structure of the South American plate. Key Points: Afterslip caused by the 2016 Pedernales earthquake requires heterogeneous fault frictional propertiesModeling 5 years of continuous Global Positioning System data suggests a 45‐km thick lithosphere overlying a Burgers body asthenosphere with Maxwell viscosity = 3 × 1019 Pa sThe frictional property variability along the Ecuador‐Colombia trench likely persists throughout the whole earthquake cycle [ABSTRACT FROM AUTHOR]

The city of Chone, being situated on the Ecuadorian coast, was affected due to the close-by epicenter of the earthquake of 16 April 2016, which reached a magnitude of Mw 7.8. This catastrophic event presented settlements in the ground, sand boils and land subsidence, being the most damaging in a variety of civil works among these several buildings. The main objective of the current study is to select data using the standard penetration test (SPT) for the evaluation of the probability of liquefaction considering a maximum acceleration seismic risk of amax = 0.5 g. With the tabulated information, a liquefaction hazard map was generated for the city of Chone, where a safety factor of 1228 was obtained, determining the potentially liquefiable strata at an approximate depth between 9 and 11 m. Hereby, we were able to demonstrate results that were obtained experimentally through a quantitative analysis, indicating that the urban area of the city of Chone has a high probability of liquefaction, which was supported due to the presence of Holocene-aged soils developed in alluvial deposits, located in an alluvium mid catchment area. This novel research, due to the combination of a variety of used tools in the seismic risk evaluation, provides a relevant contribution to territorial planning and risk management in construction, in addition to the territorial reorganization of the canton as an example for different regions worldwide with similar geodynamics, soil mechanics and seismic vulnerabilities. [ABSTRACT FROM AUTHOR]

The city of Portoviejo in coastal Ecuador was severely affected during the 16 April 2016, Pedernales earthquake (Mw 7.8). Various coseismic liquefaction phenomena occurred, inducing lateral spreading, sand boils, ground subsidence, and sinkholes in soils with poor geotechnical quality in the alluvial and alluvial–colluvial sedimentary environment. Therefore, the main aim of this study was to collect data from standard penetration tests (SPT) and shear velocity and exploratory trenches and to calculate the liquefaction potential index (LPI) by considering a corresponding seismic hazard scenario with an amax = 0.5 g. From these data, a liquefaction hazard map was constructed for the city of Portoviejo, wherein an Fs of 1.169 was obtained. It was determined that strata at a depth of between 8 and 12 m are potentially liquefiable. Our quantitative results demonstrate that the city of Portoviejo's urban area has a high probability of liquefaction, whereas the area to the southeast of the city is less sensitive to liquefaction phenomena, due to the presence of older sediments. Our results are in accordance with the environmental effects reported in the aftermath of the 2016 earthquake. [ABSTRACT FROM AUTHOR]

The city of Chone, being situated on the Ecuadorian coast, was affected due to the close-by epicenter of the earthquake of 16 April 2016, which reached a magnitude of Mw 7.8. This catastrophic event presented settlements in the ground, sand boils and land subsidence, being the most damaging in a variety of civil works among these several buildings. The main objective of the current study is to select data using the standard penetration test (SPT) for the evaluation of the probability of liquefaction considering a maximum acceleration seismic risk of amax = 0.5 g. With the tabulated information, a liquefaction hazard map was generated for the city of Chone, where a safety factor of 1228 was obtained, determining the potentially liquefiable strata at an approximate depth between 9 and 11 m. Hereby, we were able to demonstrate results that were obtained experimentally through a quantitative analysis, indicating that the urban area of the city of Chone has a high probability of liquefaction, which was supported due to the presence of Holocene-aged soils developed in alluvial deposits, located in an alluvium mid catchment area. This novel research, due to the combination of a variety of used tools in the seismic risk evaluation, provides a relevant contribution to territorial planning and risk management in construction, in addition to the territorial reorganization of the canton as an example for different regions worldwide with similar geodynamics, soil mechanics and seismic vulnerabilities.

The city of Portoviejo in coastal Ecuador was severely affected during the 16 April 2016, Pedernales earthquake (Mw 7.8). Various coseismic liquefaction phenomena occurred, inducing lateral spreading, sand boils, ground subsidence, and sinkholes in soils with poor geotechnical quality in the alluvial and alluvial–colluvial sedimentary environment. Therefore, the main aim of this study was to collect data from standard penetration tests (SPT) and shear velocity and exploratory trenches and to calculate the liquefaction potential index (LPI) by considering a corresponding seismic hazard scenario with an amax = 0.5 g. From these data, a liquefaction hazard map was constructed for the city of Portoviejo, wherein an Fs of 1.169 was obtained. It was determined that strata at a depth of between 8 and 12 m are potentially liquefiable. Our quantitative results demonstrate that the city of Portoviejo’s urban area has a high probability of liquefaction, whereas the area to the southeast of the city is less sensitive to liquefaction phenomena, due to the presence of older sediments. Our results are in accordance with the environmental effects reported in the aftermath of the 2016 earthquake.

The fundamental period of structures is a parameter used in structure under design and for evaluating existing structures. Data-driven methods using ambient vibrations have become popular, particularly for the adjustment of empirical relationships applied to building classes. This study presents the results of a survey of ambient vibrations performed in 146 reinforced concrete buildings in the center of Quito (Ecuador). Classical functional forms giving period (T) for height (H) or number of floors (N) are derived and compared with the relationships available in the Ecuadorian seismic design provisions. We highlight variations in the empirical relationships according to soil conditions, but above all according to the date of construction and the historic seismic sequence to which the buildings have been exposed. The cumulative damage effect is finally confirmed by repeating ambient vibration measurements after the 2016 Mw 7.8 Pedernales earthquake located in the subduction zone, about 175 km from Quito. Even with such a long epicentral distance, leading to low macroseismic intensity (IEMS98 = IV), the seismic ground motion of between 0.017 and 0.081 g recorded in Quito reduced the resonant frequency of the buildings tested by between 2 and 13%. This confirms the effect of cumulative damage in reinforced concrete buildings located in seismic zones, even for weak ground motions, and the variability of empirical T/H relationships associated with damage. [ABSTRACT FROM AUTHOR]

Seismically induced soil liquefaction has been documented after the M7.8, 2016 Pedernales earthquake. In the city of Jama, the acceleration recorded by soil amplification yielded 1.05 g with an intensity of VIII to IXESI-07. The current study combines geological, geophysical, and geotechnical data in order to establish a geological characterization of the subsoil of the city of Jama in the Manabi province of Ecuador. Then, the liquefaction potential index (LPI) has been evaluated considering the PGA-rock values calculated from deterministic methods applied to nearby geological faults, as well as the soil acceleration records for the city of Jama since the Pedernales megathrust earthquake. The importance of conducting geotechnical evaluations of particular colluvial, alluvial, and floodplain deposits, for which the liquefaction probability profiles have been additionally obtained, may serve as a useful tool for edifices foundations or earthquake resistant designs. Finally, the site response analysis is presented using a linear equivalent analysis, where previously seismic records compatible with the target spectrum have been selected. Hereby, the results of ground surface effects have been compared with the spectra of the Ecuadorian Regulation of Construction (NEC) in the context of local seismic amplification.

The northern Ecuador segment of the Nazca/South America subduction zone shows spatially heterogeneous interseismic coupling. Two highly coupled zones (0.4° S–0.35° N and 0.8° N–4.0° N) are separated by a low coupled area, hereafter referred to as the Punta Galera-Mompiche Zone (PGMZ). Large interplate earthquakes repeatedly occurred within the coupled zones in 1958 (Mw 7.7) and 1979 (Mw 8.1) for the northern patch and in 1942 (Mw 7.8) and 2016 (Mw 7.8) for the southern patch, while the whole segment is thought to have rupture during the 1906 Mw 8.4–8.8 great earthquake. We find that during the last decade, the PGMZ has experienced regular and frequent seismic swarms. For the best documented sequence (December 2013–January 2014), a joint seismological and geodetic analysis reveals a six-week-long Slow Slip Event (SSE) associated with a seismic swarm. During this period, the microseismicity is organized into families of similar earthquakes spatially and temporally correlated with the evolution of the aseismic slip. The moment release (3.4 × 10 18 Nm, Mw 6.3), over a ~ 60 × 40 km area, is considerably larger than the moment released by earthquakes (5.8 × 10 15 Nm, Mw 4.4) during the same time period. In 2007–2008, a similar seismic-aseismic episode occurred, with higher magnitudes both for the seismic and aseismic processes. Cross-correlation analyses of the seismic waveforms over a 15 years-long period further suggest a 2-year repeat time for seismic swarms, which also implies that SSEs recurrently affect this area. Such SSEs contribute to release the accumulated stress, likely explaining why the 2016 Pedernales earthquake did not propagate northward into the PGMZ. [ABSTRACT FROM AUTHOR]

We provide a dataset of the landslides induced by the 2016 Pedernales megathrust earthquake, Ecuador (Mw 7.8, focal depth of 20 km) and compare their spatial distribution with mapped bedrock lithology, horizontal peak ground acceleration (PGA-h) and the macroseismic intensity based on earthquake-induced environmental effects (ESI-07). We studied 192 coseismic landslides (classified as coherent, disrupted and lateral spreads) located in the epicentral area, defined by the VII to IXESI-07 isoseismals. Based on our findings, lahar deposits, tuffs and volcanoclastic units are the most susceptible to landslides occurrence. Alluvial plains with fluvial loose fine sand are the most susceptible setting for lateral spreading, with a maximum intensity of IXESI-07. The coherent landslides are frequently found in altered shale and siltstone geological units with moderate slopes (8°−16°), with typical intensity ranging between VII and VIIIESI-07. Our analysis draws a typical framework for slope movements triggered by subduction earthquakes in Ecuador. The most dangerous setting is the coastal region, a relatively highly urbanized area located near the epicenter and where liquefaction can trigger massive lateral spreading events. Coherent and disrupted landslides, dominating the more internal hilly region, can be triggered also in moderate slope settings (i.e., less than 10°). Indeed, the regression analysis between seismic intensity, PGA-h and landslide occurrence shows that most of the events occurred at PGA-h values between 0.4 g and 1.2 g, at a distance of 30 to 50 km from the rupture plane. Our database suggests that lithology and hillslope geometry are the main geological/geomorphological factors controlling coseismic landslides occurrence; while the distance from the rupture plane plays a significant role on determining the landslide size. Finally, we underline that coseismically-triggered landslides are among the most common environmental effects occurring during large subduction events that can be effectively used to properly evaluate the earthquake macroseismic field. The landslide inventory we compiled is suitable for assessing the vulnerability of physical environment from subduction earthquakes in Ecuador, and offers a primary data source for future worldwide analysis.

The 2016 Pedernales earthquake (Mw 7.8), is part of the sequence of large earthquakes in Ecuador and Colombia: 1906 (~8.8 Mw), 1942 (Mw 7.8), 1958 (Mw 7.7), 1979 (Mw 8.2), all these events with a focal mechanism of the thrust fault type. In this research, we have obtained the seismic source distribution (indicating the presence of 2 main asperities), from inversion of teleseismic signals, as well as the parameters of the seismic rupture process: focal mechanism that indicates a type of inverse fault (strike = 25∘, dip = 12∘, rake = 118∘) for a focal depth of 23 km and the source time function indicating a composite event, the duration of the rupture process was around 70 s, assuming an average rupture velocity of 3.0 km/s. The seismic moment was calculated at 5.77×1020 Nm, equivalent to a magnitude of Mw 7.8. The smallest asperity is located around the epicentre and the main asperity is located around the coastline to the south-west from the epicentre. The maximum dislocation or slip was 3.75 m. The coseismic vertical displacement is not conductive to the generation of a large tsunami, as it is around 1 m only. The zone of Pedernales have a Coulomb stress transfer of 22 bar, therefore, this area is loaded with stresses and is a potentially seismic zone for an upcoming earthquake. • The slip distribution for the 2016 Ecuador earthquake was calculated. • The teleseismic waveform inversion method was used. • The deformation field pattern and the Coulom stress tranfer was obtained. [ABSTRACT FROM AUTHOR]

Seismically induced soil liquefaction has been documented after the M7.8, 2016 Pedernales earthquake. In the city of Jama, the acceleration recorded by soil amplification yielded 1.05 g with an intensity of VIII to IXESI-07. The current study combines geological, geophysical, and geotechnical data in order to establish a geological characterization of the subsoil of the city of Jama in the Manabi province of Ecuador. Then, the liquefaction potential index (LPI) has been evaluated considering the PGA-rock values calculated from deterministic methods applied to nearby geological faults, as well as the soil acceleration records for the city of Jama since the Pedernales megathrust earthquake. The importance of conducting geotechnical evaluations of particular colluvial, alluvial, and floodplain deposits, for which the liquefaction probability profiles have been additionally obtained, may serve as a useful tool for edifices foundations or earthquake resistant designs. Finally, the site response analysis is presented using a linear equivalent analysis, where previously seismic records compatible with the target spectrum have been selected. Hereby, the results of ground surface effects have been compared with the spectra of the Ecuadorian Regulation of Construction (NEC) in the context of local seismic amplification. [ABSTRACT FROM AUTHOR]

We provide a dataset of the landslides induced by the 2016 Pedernales megathrust earthquake, Ecuador (Mw 7.8, focal depth of 20 km) and compare their spatial distribution with mapped bedrock lithology, horizontal peak ground acceleration (PGA-h) and the macroseismic intensity based on earthquake-induced environmental effects (ESI-07). We studied 192 coseismic landslides (classified as coherent, disrupted and lateral spreads) located in the epicentral area, defined by the VII to IXESI-07 isoseismals. Based on our findings, lahar deposits, tuffs and volcanoclastic units are the most susceptible to landslides occurrence. Alluvial plains with fluvial loose fine sand are the most susceptible setting for lateral spreading, with a maximum intensity of IXESI-07. The coherent landslides are frequently found in altered shale and siltstone geological units with moderate slopes (8°–16°), with typical intensity ranging between VII and VIIIESI-07. Our analysis draws a typical framework for slope movements triggered by subduction earthquakes in Ecuador. The most dangerous setting is the coastal region, a relatively highly urbanized area located near the epicenter and where liquefaction can trigger massive lateral spreading events. Coherent and disrupted landslides, dominating the more internal hilly region, can be triggered also in moderate slope settings (i.e., less than 10°). Indeed, the regression analysis between seismic intensity, PGA-h and landslide occurrence shows that most of the events occurred at PGA-h values between 0.4 g and 1.2 g, at a distance of 30 to 50 km from the rupture plane. Our database suggests that lithology and hillslope geometry are the main geological/geomorphological factors controlling coseismic landslides occurrence; while the distance from the rupture plane plays a significant role on determining the landslide size. Finally, we underline that coseismically-triggered landslides are among the most common environmental effects occurring during large subduction events that can be effectively used to properly evaluate the earthquake macroseismic field. The landslide inventory we compiled is suitable for assessing the vulnerability of physical environment from subduction earthquakes in Ecuador, and offers a primary data source for future worldwide analysis. [ABSTRACT FROM AUTHOR]