nasa-gesdisc/es-publications-researchareas huggingface dataset:
Repeating nontectonic seasonal stress changes and a possible triggering mechanism of the 2019 Ridgecrest earthquake sequence in California (2021)

Here we characterize the 13-year history of nontectonic horizontal strain anomalies across the regions surrounding Ridgecrest, CA, using cGPS data from January 2007. This time-dependent model reveals a seasonality in the nontectonic strain anomalies and the associated Coulomb stress changes of ∼±0.5-2 kPa. In the area surrounding the epicenters of the 2019 Ridgecrest earthquake sequence of July, we find that the seasonal preseismic Coulomb stress changes peaked every early summer (May and June) during the last 13 years including during June 2019, a month prior to the large events. In addition, our statistical tests confirm that more strike-slip earthquakes (M<SUB>w</SUB> ≥ 2) occur during times when seasonal stress changes are increasing on right-lateral faults in comparison with times when stresses are decreasing. These results suggest that the timing of the 2019 Ridgecrest earthquakes may have been modulated by nontectonic seasonal stress changes. The dynamic source of the seasonal nontectonic strain/stress anomalies, however, remains enigmatic. We discuss a possible combination of driving forces that may be attributable for the seasonal variations in nontectonic strain/stress anomalies, which captured in cGPS measurements.

Research areas: Earthquakes
Sensitivity of the International Monitoring System infrasound network to elevated sources: a western Eurasia case study (2017)

For the past 5 years (20102015) infrasound arrivals have been included in International Data Centre analyst-reviewed bulletins of events detected across the International Monitoring System (IMS). In western Eurasia, there are clusters of up to 268 events that consist of only infrasound arrivals (no associated seismic phases). These clusters are of unknown origin, although one in the North Sea region is associated with sonic booms from supersonic aircraft activity. IMS data for 17 North Sea events are analysed and compared with data from the Large Aperture Infrasound Array in the Netherlands to support the existence of these events and to determine common characteristics. Three other large clusters in western Eurasia are also identified and studied and show similar characteristics to the North Sea events, indicative of supersonic aircraft activity. The IMS infrasound network is shown to be particularly sensitive to sonic booms because the elevated source height reduces the anisotropy of infrasonic propagation within a stratospheric duct and allows for episodic upwind propagation. This episodic upwind propagation in addition to the prevailing downwind propagation, leads to clusters of Reviewed Event Bulletin events with constrained locations in western Eurasia region during the summer months. In the winter months, the recorded arrivals suggest that episodic upwind propagation is not as prevalent. Propagation modelling indicates that the subsequent unidirectional propagation, combined with the sparseness of the IMS network, leads to elongated lines of estimated event locations.

Research areas: Earthquakes
Seismic hazard and risk assessment based on Unified Scaling Law for Earthquakes: thirteen principal urban agglomerations of India (2018)

The deterministic seismic hazard map of India with spatially distributed peak ground acceleration was used to estimate seismic risk using two data sets of the Indian populationthe model population data set and the data set based on Indias Census 2011. Four series of the earthquake risk maps of the region based on these two population density sets were cross-compared. The discrepancy of the population data and seismic risks estimation were illuminated for the thirteen principal urban agglomerations of India. The confirmed fractal nature of earthquakes and their distribution in space implies that traditional probabilistic estimations of seismic hazard and risks of cities and urban agglomerations are usually underestimated. The evident patterns of distributed seismic activity follow the Unified Scaling Law for Earthquakes, USLE, which generalizes GutenbergRichter recurrence relation. The results of the systematic global analysis imply that the occurrence of earthquakes in a region is characterized with USLE: log10N (M, L) = A + B  (5  M) + C  log10L, where N(M, L)expected annual number of earthquakes of magnitude M within an area of liner size L, A determines seismic static rate, Bbalance between magnitude ranges, and Cfractal dimension of seismic loci. We apply the seismic hazard and risk assessment methodology developed recently based on USLE, pattern recognition of earthquake-prone geomorphic nodes, and neo-deterministic scenarios of destructive ground shaking. Objects of risk are individuals (1) as reported in the 2011 National Census data and (2) as predicted for 2010 by Gridded Population of the World (model GPWv3); vulnerability depends nonlinearly on population density. The resulting maps of seismic hazard and different risk estimates based on population density are cross-compared. To avoid misleading interpretations, we emphasize that risk estimates presented here for academic purposes only. In the matter of fact, they confirm that estimations addressing more realistic and practical kinds of seismic risks should involve experts in distribution of objects of risk of different vulnerability, i.e., specialists in earthquake engineering, social sciences, and economics.

Research areas: Earthquakes
Pre-seismic ionospheric anomalies and spatio-temporal analyses of MODIS Land surface temperature and aerosols associated with Sep, 24 2013 Pakistan … (2020)

This study aims to investigate the behaviors of the potential earthquake precursors such as Total Electron Content (TEC), daytime/nighttime Land Surface Temperature (LST) and aerosols before and after the 2013 Mw 7.7 Awaran (Pakistan) earthquake. TEC values were obtained from Global Positioning System (GPS) measurements, and LST and aerosol values were retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Terra and Aqua satellites, respectively. In order to detect the anomalies, moving median method was used in TEC analyses and 2 (95% confidence level) interval was utilized in LST and Aerosol Optical Depth (AOD) analyses as anomaly indicator. TEC anomalies were identified 3 days (21.09.2013) and 5 days (19.09.2013) before the earthquake. In daytime/nighttime LST analyses, three regions of interest for spatial analyses were determined including epicenter, 10 km impact area around the epicenter and Modified Mercalli Intensity (MMI) 7.5 contour which was presented in the United States Geological Survey (USGS)'s shake map. Different anomalous days of LST were observed from these three regions of interest. In AOD analysis, only MMI 7.5 contour was considered due to its low spatial resolution (10  10km pixel size). The anomaly in AOD values was observed on 29.09.2013, 5 days after the earthquake. However, the abnormal behavior of AOD on 21.09.2013 was consistent with GPS-TEC anomaly. Furthermore, considering daytime/nighttime LST values on epicenter and 10 km impact area, we observed a systematic increase culminated near the earthquake event and a decrease after the earthquake. On the contrary, a systematic decrease and then increase of the AOD values were identified. The obtained results showed that TEC, LST and AOD were important potential precursors for Earthquake prediction; however, further developments on methods, data types and statistical analyses are still required.

Research areas: Earthquakes
A Study from Space of Anomalous Variations of Various Geophysical Fields during the Preparation of a Series of Strong Earthquakes in Italy in 2016–2017 (2022)

A time series of the occurrence of thermal anomalies, aerosol optical-depth anomalies, and total electron content of the ionosphere during the preparation of strong earthquakes with magnitudes of M = 5.26.6 in Central Italy in 20162017 is revealed based on the joint analysis of various geophysical fields recorded from space. The values of temperatures of the surface, the near-surface layer of the atmosphere, and the outgoing longwave radiation detected by the AIRS instrument (Aqua satellite) are used to analyze thermal fields. Changes in the aerosol optical-depth values are investigated using the MCD19A2 product (Terra and Aqua satellites). Global ionospheric maps obtained from data of global satellite navigation systems and ground-based GPS stations located within a radius of 100 km from earthquake epicenters are used to study anomalies in the ionosphere. It is found that the first precursory changes in geophysical fields occurred in areas with radii of 200 km, the centers of which coincided with the centers of high earthquake risk zones, and were detected 1115 days before the main seismic shocks.

Research areas: Earthquakes
Buried aseismic slip and off‐fault deformation on the southernmost San Andreas fault triggered by the 2010 El Mayor Cucapah earthquake revealed by UAVSAR (2021)

We use UAVSAR interferograms to characterize fault slip, triggered by the Mw 7.2 El Mayor-Cucapah earthquake on the 1 San Andreas Fault in the Coachella Valley providing comprehensive maps of short-term geodetic surface deformation that complement in situ measurements. Creepmeters and geological mapping of fault offsets on Durmid Hill recorded 4 and 8 mm of average triggered slip respectively on the fault, in contrast to radar views that reveal significant off-fault dextral deformation averaging 20 mm. Unlike slip in previous triggered slip events on the southernmost San Andreas fault, dextral shear in 2010 is not confined to transpressional hills in the Coachella valley. Edge detection and gradient estimation applied to the 50-m-sampled interferogram data identify the location (to 20 m) and local strike (to &lt;4°) of secondary surface ruptures. Transverse curve fitting applied to these local detections provides local estimates of the radar-projected dextral slip and a parameter indicating the transverse width of the slip, which we equate with the depth of subsurface shear. These estimates are partially validated by fault-transverse interferogram profiles generated using the GeoGateway UAVSAR tool, and appear consistent for radar-projected slip greater than about 5 mm. An unexpected finding is that creep and triggered slip on the San Andreas fault terminate in the shallow subsurface below a surface shear zone that resists the simple expression of aseismic fault slip. We introduce the notion of a surface locking depth above which fault slip is manifest as distributed shear, and evaluate its depth as 6-27 m.

Research areas: Earthquakes
Real-time impact analysis and response using a new disaster metrics: 2018 Sulawesi (Indonesia) earthquake and tsunami (2020)

Introduction:The Richter Scale measures the magnitude of the seismic activity for an earthquake; however, it does not quantify the humanitarian need at the point of impact. This poses a challenge for humanitarian stakeholders in decision and policy making, especially in risk reduction, response, recovery, and reconstruction. The new disaster metrics tool titled The YEW Disaster Severity Index (DSI) was developed and presented at the 2017 World Congress of Disaster and Emergency Medicine, May 2017, Toronto, Canada. It uses a median score of three for vulnerability and exposure indicators, a median score percentage of 100%, and medium YEW DSI scoring of four to five as baseline, indicating the ability to cope within local capacity. Therefore, scoring more than baseline coping capacity indicates that external assistance is needed. This special real-time report was presented at the 2nd National Pre-Hospital Care Conference and Championship, October 2018, Malaysia.Report:The aim of this analysis is to present the real-time humanitarian impact and response to the 2018 earthquake and tsunami at Donggala and Palu, Sulawesi in Indonesia using the new disaster metrics YEW DSI. Based on the earthquake (measuring 7.7 on the Richter Scale) and tsunami at Donggala, the humanitarian impact calculated on September 29, 2018 scored 7.4 High in the YEW DSI with 11 of the total 17 indicators scoring more than the baseline coping capacity. The same YEW DSI score of 7.4 was scored on the earthquake and tsunami at Palu, with 13 of the total 17 indicators scoring more than baseline ability to cope within local capacity. Impact analysis reports were sent to relevant authorities on September 30, 2018.Discussion & Conclusion:A State of Emergency was declared for a national response, which indicated an inability to cope within the local capacity, shown by the YEW DSI. The strong correlation between the earthquake magnitude, intensities, and the humanitarian impact at Donggala and Palu reported could be added into the science of knowledge in prehospital care and disaster medicine research and practice. As a conclusion, the real-time disaster response was found to be almost an exact fit with the YEW DSI indicators, demonstrating the inability to cope within the local capacity.

Research areas: Earthquakes
Shallow crustal imaging using distant, high-magnitude earthquakes (2019)

Global phases, viz. seismic phases that travel through the Earths core, can be used to locally image the crust by means of seismic interferometry. This method is known as Global Phase Seismic Interferometry (GloPSI). Traditionally, GloPSI retrieves low-frequency information (up to 1 Hz). Recent studies, however, suggest that there is high-frequency signal present in the coda of strong, distant earthquakes. This research quantifies the potential of these high-frequency signals, by analysing recordings of a multitude of high-magnitude earthquakes (6.4 Mw) and their coda on a selection of permanent USArray stations. Nearly half of the P, PKP and PKIKP phases are recorded with a signal-to-noise ratio of at least 5 dB at 3 Hz. To assess the viability of using the high-frequency signal, the second half of the paper highlights two case studies. First, a known sedimentary structure is imaged in Malargue, Argentina. Secondly, the method is used to reveal the structure of the Midcontinent Rift below the SPREE array in Minnesota, USA. Both studies demonstrate that structural information of the shallow crust (5 km) below the arrays can be retrieved. In particular, the interpreted thickness of the sedimentary layer below the Malargue array is in agreement with earlier studies in the same area. Being able to use global phases and direct P-phases with large epicentral distances (>80) to recover the Earths sedimentary structure suggests that GloPSI can be applied in an industrial context.

Research areas: Earthquakes
New Maps of Global Geological Provinces and Tectonic Plates (2022)

Accurate spatial models of tectonic plates and geological terranes are important for analyzing and interpreting a wide variety of geoscientific data and developing compositional and physical models of the lithosphere. We present a global compilation of active plate boundaries and geological provinces in a shapefile format with interpretive attributes (e.g., crust type, plate type, province type, last orogeny). The initial plate and province boundaries are constructed from a combination of published global and regional models that we refine using a variety of geoscientific constraints including, but not limited to, relative GPS motions, earthquakes, mapped faults, potential field characteristics, and geochronology. These new plate model show improved correlation to observed earthquake and volcano occurrences within deformation zones and microplates, compared to existing models, capturing 73 and 80% of these criteria, respectively. Deformation zones and microplates only account for 16% of Earth's surface area. We estimate 57.5% of the Earth's surface is covered by oceanic crust, which is a slight increase relative to the most recent seafloor age model. The model of last orogenies agrees well with peaks in the globally summed geochronology data. There is room for improvement in future editions of our global plate and geologic provinces model where basins, ice, or lack of geological data fidelity obscure bedrock geology, particularly in the eastern Central Asian Orogenic Belt, much of Africa, East Antarctica, and eastern Australia. Additionally, some province types-orogens, shields, and cratons that are homogenized within our global scheme-can likely be partitioned into smaller terranes with more precise geodynamic attributes. Despite some of these shortcomings, the digital maps presented here form a self-consistent data standard for adding spatial metadata to geoscientific databases. The database is available on GitHub where the geoscience community can provide updates to improve the models and their contemporaneity as new knowledge is acquired. The files are also released in formats suitable for use in Generic Mapping Tools and GoogleEarth.

Research areas: Land Surface/Agriculture Indicators, Earthquakes
Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures (2020)

Human activity causes vibrations that propagate into the ground as high-frequency seismic waves. Measures to mitigate the coronavirus disease 2019 (COVID-19) pandemic caused widespread changes in human activity, leading to a months-long reduction in seismic noise of up to 50%. The 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record. Although the reduction is strongest at surface seismometers in populated areas, this seismic quiescence extends for many kilometers radially and hundreds of meters in depth. This quiet period provides an opportunity to detect subtle signals from subsurface seismic sources that would have been concealed in noisier times and to benchmark sources of anthropogenic noise. A strong correlation between seismic noise and independent measurements of human mobility suggests that seismology provides an absolute, real-time estimate of human activities.

Research areas: Earthquakes
Variable-resolution building exposure modelling for earthquake and tsunami scenario-based risk assessment: an application case in Lima, Peru (2021)

Abstract. We propose the use of variable resolution boundaries based on central Voronoi tessellations (CVTs) to spatially aggregate building exposure models for risk assessment to various natural hazards. Such a framework is especially beneficial when the spatial distribution of the considered hazards presents intensity measures with contrasting footprints and spatial correlations, such as in coastal environments. This work avoids the incorrect assumption that a single intensity value from hazards with low spatial correlation (e.g. tsunami) can be considered to be representative within large-sized geo-cells for physical vulnerability assessment, without, at the same time, increasing the complexity of the overall model. We present decoupled earthquake and tsunami scenario-based risk estimates for the residential building stock of Lima (Peru). We observe that earthquake loss models for far-field subduction sources are practically insensitive to the exposure resolution. Conversely, tsunami loss models and associated uncertainties depend on the spatial correlations of the hazard intensities as well as on the resolution of the exposure models. We note that for the portfolio located in the coastal area exposed to both perils in Lima, the ground shaking dominates the losses for lower-magnitude earthquakes, whilst tsunamis cause the most damage for larger-magnitude events. For the latter, two sets of existing empirical flow depth fragility models are used, resulting in large differences in the calculated losses. This study, therefore, raises awareness about the uncertainties associated with the selection of fragility models and spatial aggregation entities for exposure modelling and loss mapping.

Research areas: Earthquakes
Study of 28th April, 2021 Mw 6.0 Assam earthquake in a part of eastern Himalayan foreland region, northeast India (2022)

The northeastern part of India is seismically very active due to the ongoing Indian Plate under-thrusting and rise of several mountain ranges. As a result, the Himalayas, Naga Hills, Shillong-Karbi Massifs, and the Assam Valley have many crustal-scale active faults. These faults often cause moderate to large earthquakes while releasing the accumulated stress associated with Plate tectonics. In this study, one such major earthquake event of Mw 6.0 occurred near the Kopili Fault and Himalayan Frontal Thrust in the eastern Himalayan foreland region on 28th April 2021. The event has been investigated to understand its seismotectonic and environmental impacts. The quake caused much damage in the epicentral area around Dhekiyajuli of Sonitpur District, Assam, India. The densely populated Guwahati and Tezpur cities of Assam have suffered damage as some parts of buildings and roads were collapsed. Moreover, a landslide near Bhairabkunda and several liquefaction incidents near Tezpur and Dhekiyajuli localities were also recorded, within 3050 km from the epicentre. It is found from NASA's GRACE-Land data that the increase in groundwater volume on the northern bank of the Brahmaputra than the previous year might be related to higher rainfall in the recharge zone around the Himalayan Frontal parts. Such groundwater conditions caused saturation of the subsurface soil and alluvium, which resulted in the formation of liquefaction during high shaking. These incidents also caused severe environmental damage. After the earthquake, the sprouting of mud water affected rice fields and nearby freshwater sources like ponds and lakes. This earthquake, along with the historical ones, reveals the vulnerability of the entire region to many natural hazards. This study provides a scope to understand the seismotectonic and environmental exposure of the eastern Himalayan foothill region.

Research areas: Earthquakes
Seasonal modulation of oceanic seismicity in the azores (2022)

The analysis of an 11-year (20082018) seismic catalogue of the Azores suggests the existence of secondary cyclic influences on the seismicity rate of the oceanic region, with more earthquakes observed during the summer months, from May to August, than in winter. Statistical testing based on Monte-Carlo simulations and a Jack-Knife methodology indicate that the seasonal modulation affects earthquakes with magnitudes M3.34.5, well above the magnitude of completeness. Here, we investigate the seasonal variations of earthquake rate considering both the whole Azores oceanic domain and four separate sub-regions, corresponding to four regional clusters identified by previous authors. The analysis shows that the seasonal modulation is particularly observed near the Triple Junction region between the Faial Island and the Mid-Atlantic Ridge. To identify possible mechanisms driving the seasonal modulation, we apply Singular Spectral Analysis to the seismicity rate and to time-series of plausible external triggers, in order to investigate possible common periodicities. We find significant correlations between the earthquake rate, sea level anomaly rate, GRACE satellite anomalies and ocean bottom pressure, suggesting that water load may modulate the Azores oceanic seismicity.

Research areas: Earthquakes
Earthquake science in resilient societies (2017)

Earthquake science is critical in reducing vulnerability to a broad range of seismic hazards. Evidence-based studies drawing from several branches of the Earth sciences and engineering can effectively mitigate losses experienced in earthquakes. Societies that invest in this research have lower fatality rates in earthquakes and can recover more rapidly. This commentary explores the scientific pathways through which earthquake-resilient societies are developed. We highlight recent case studies of evidence-based decision making and how modern research is improving the way societies respond to earthquakes.

Research areas: Earthquakes