nasa-gesdisc/es-publications-researchareas huggingface dataset:
Earthquake magnitudes from dynamic strain (2021)

Dynamic strains have never played a role in determining local earthquake magnitudes, which are routinely set by displacement waveforms from seismic instrumentation (e.g., ML). We present a magnitude scale for local earthquakes based on broadband dynamic strain waveforms. This scale is derived from the peak rootmeansquared strains (A) in 4589 records of dynamic strain associated with 365 crustal earthquakes and 77 borehole strainmeters along the PacificNorth American plate boundary on the west coast of the United States and Canada. In this data set, catalog moment magnitudes range from 3.5Mw7.2, and hypocentral distances range from 6R500  km. The 1D representation of geometrical spreading and attenuation of A common to all strain data is logA0(R)=0.00072R1.45log(R). After correcting for instrument gain, site terms, and event terms, the magnitude scale, MDS=logAlogA0(R)log(3109), scales as 0.92Mw with a residual standard deviation of 0.19. This close association with Mw holds for events east of the 124 meridian; west of this boundary, however, a constant correction of 0.41 is needed to adjust for additional alongpath attenuation effects. As a check on the accuracy of this magnitude scale, we apply it to dynamic strain records from three strainmeters located in the near field of the 2019 M 6.4 and 7.1 Ridgecrest earthquakes. Results from these six records are in agreement to within 0.5 magnitude units, and five out of six records are in agreement to within 0.34 units.

Research areas: Earthquakes
Morphotectonics and Late Quaternary Seismic Stratigraphy of Lake Garda (Northern Italy) (2020)

Lake Garda, the largest lake in Italy at the southern front of the central Alps, provides a unique opportunity to reconstruct Quaternary geological processes related to the interplay between deglaciation driven sedimentation and tectonic activity. In fact, the topographic depression presently occupied by the lake was site of a major glacial tongue during the LGM, and is located close to the epicentral areas of two of the largest magnitude historical earthquakes recorded in the Po Plain, the Verona (Jan. 13, 1117) and Brescia, (Dec. 25, 1222) seismic events, characterized by Io IX-X MCS, respectively. Despite this peculiarity, geophysical surveys of the lake are scant. We present results of a waterborne geophysical survey of Lake Garda, leading to the acquisition of a densely-spaced grid of high-resolution seismic reflection profiles which image the lake floor and uppermost sedimentary sequence. These data enabled us to compile thematic maps which provide insights on active geologic processes in different sectors of the basin. We focused our work on a prominent seismic reflector (H1), correlated over the entire lake surface, to estimate the sediment deposition rate at the scale of the last 10 ka, and to evaluate the variability of seismic facies and geological processes in different sectors of the basin. Based on available stratigraphic data, we discuss whether H1 could mark the diachronic glacial/fluvio-glacial transition after the Last Glacial Maximum, when the ice tongues south of the Alps started to melt and collapse. We observed that sediments of the southern Lake Garda are affected by incipient tectonic deformation, and two major seismoturbidite-homogenite beds might represent over 50% of the Holocene sedimentary record in the lake depocenter, making the study of the Lake Garda stratigraphy an interesting tool for assessing earthquake hazards at the southern front of the Alpine chain.

Research areas: Earthquakes
Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity (2018)

We observe remarkably periodic patterns of seismicity rates and magnitudes at the Fimbul Ice Shelf, East Antarctica, correlating with the cycles of the ocean tide. Our analysis covers 19 years of continuous seismic recordings from Antarctic broadband stations. Seismicity commences abruptly during austral summer 2011 at a location near the ocean front in a shallow water region. Dozens of highly repetitive events occur in semi-diurnal cycles, with magnitudes and rates fluctuating steadily with the tide. In contrast to the common unpredictability of earthquake magnitudes, the event magnitudes show deterministic trends within single cycles and strong correlations with spring tides and tide height. The events occur quasi-periodically and the highly constrained event sources migrate landwards during rising tide. We show that a simple, mechanical model can explain most of the observations. Our model assumes stick-slip motion on a patch of grounded ice shelf, which is forced by the variations of the ocean-tide height and ice flow. The well fitted observations give new insights into the general process of frictional triggering of earthquakes, while providing independent evidence of variations in ice shelf thickness and grounding.

Research areas: Earthquakes
Analysis of Faster-Than-Real-Time (FTRT) Tsunami Simulations for the Spanish Tsunami Warning System for the Atlantic (2022)

Real-time local tsunami warnings embody uncertainty from unknowns in the source definition within the first minutes after the tsunami generates. In general, Tsunami Warning Systems (TWS) provide a quick estimate for tsunami action from deterministic simulations of a single event. In this study, variability in tsunami source parameters has been included by running 135 tsunami simulations; besides this, four different computational domains in the northeastern Atlantic ocean have been considered, resulting in 540 simulations associated with a single event. This was done for tsunamis generated by earthquakes in the Gulf of Cadiz with impact in the western Iberian peninsula and the Canary Islands. A first answer is provided after one minute, and 7 min are required to perform all the simulations in the four computational domains. The fast computation allows alert levels all along the coast to be incorporated into the Spanish National Tsunami Early Warning System. The main findings are that the use of a set of scenarios that account for the uncertainty in source parameters can produce higher tsunami warnings in certain coastal areas than those obtained from a single deterministic reference scenario. Therefore, this work shows that considering uncertainties in tsunami source parameters helps to avoid possible tsunami warning level underestimations. Furthermore, this study demonstrates that this is possible to do in real time in an actual TWS with the use of high-performance computing resources.

Research areas: Earthquakes
Decreasing Trend of Geohazards Induced by the 2008 Wenchuan Earthquake Inferred from Time Series NDVI Data (2019)

The occurrence of aftershocks and geohazards (landslides, collapses, and debris flows) decreases with time following a major earthquake. The 12 May 2008 Wenchuan Earthquake in Sichuan, China, provides the opportunity to characterize the subsequent spatiotemporal evolution of geohazards. Following the 12 May 2008 Wenchuan Earthquake, the incidence of geohazards first increased sharply, representing a post-earthquake effect, before starting to decrease. We compared the spatial distribution of the area affected by vegetation damage (AVD) triggered by large and medium-scale geohazards (LMG). We studied the interval prior to the 12 May 2008 Wenchuan Earthquake (20012007), the co-seismic period (2008), and the post-earthquake interval (20092016) and characterized the trend of decreasing geohazards at a macro scale. In vegetated areas, geohazards often seriously damage the vegetation, resulting in pronounced contrasts with the surrounding surface in terms of color tone, texture, morphology, and Normalized Difference Vegetation Index (NDVI) which are evident in remote sensing images (RSI). In principle, it is possible to use the strong positive correlation between AVD and geohazards to determine indirectly the resulting vegetation and to monitor its spatiotemporal evolution. In this study we attempted to characterize the process of geohazard evolution in the region affected by the 12 May 2008 Wenchuan Earthquake during 20012016. Our approach was to analyze the characteristics of areas with reduced vegetation coverage caused by LMG. Our principal findings are as follows: (i) Before the Wenchuan Earthquake (during 20012007), there was no evidence for a linear increase in the number of LMG with time; thus, the geological environment was relatively stable and the geohazards were mainly induced by rainfall events. (ii) The 12 May 2008 Wenchuan Earthquake was the main cause of a surge in geohazards in 2008, with the characteristics of seismogenic faults and strong aftershocks determining the spatial distribution of geohazards. (iii) Following the 12 May 2008 Wenchuan Earthquake (during 20092016) the incidence of geohazards exhibited an oscillating pattern of attenuation, with a decreasing trend of higher-grade seismic intensity. The intensity of geohazards was related to rainfall and seismogenic faults, and also to the number, magnitude and depth of new earthquakes following the 12 May 2008 Wenchuan Earthquake. Our results provide a new perspective on the temporal pattern of attenuation of seismic geohazards, with implications for disaster prevention and mitigation and ecological restoration in the areas affected by the 12 May 2008 Wenchuan Earthquake.

Research areas: Earthquakes
A new model for the segmentation, propagation and linkage of the Tan-Lu fault zone, East Asia (2023)

The Tan-Lu fault zone (TLF) is a major strike-slip fault with a long and complex history in East Asia, whose evolution provides a new perspective on the formation of large-scale faults (>1000 km long). Fault displacement analysis, geological mapping and U-Pb LA-ICP-MS dating have been performed to understand the evolution of the TLF. Along-strike displacement variation reveals that the TLF consists of two kinematically independent segments, the northern and southern TLF, with opposite long-term propagation directions. Structural and geochronological studies in the eastern Yanshan belt, located around the linkage area of the southern and northern TLF, indicate that NNE-trending sinistral strike-slip faults initiated at 167164 Ma and were reactivated at 124121 Ma. Structural analysis suggests that these early NNE-trending strike-slip faults transferred sinistral motion along the northern TLF into southward thrusting along the Yanshan belt, representing the Middle Jurassic southern termination of the northern TLF. Our studies suggest that the through-going TLF formed when the younger southward-propagating northern TLF merged with the older northward-propagating southern TLF in the Late Jurassic. A new model is thus proposed for the Mesozoic evolution of the TLF. The initiation and southward propagation of the northern TLF is interpreted to have resulted from the southward indentation of the Siberian craton into the amalgamated Central Asian Orogenic Belt and North China block. The divergent mega-splays of the northern TLF likely resulted from westward-younging formation during the clockwise rotation of northeast Asia. Coalescence of two genetically unrelated faults could be an alternative mode for large-scale fault formation.

Research areas: Land Surface/Agriculture Indicators, Earthquakes
Fluid migration before and during slow earthquakes in the shallow Nankai subduction zone (2022)

Fluid migration in subduction zones is a key controlling factor of slow and megathrust earthquakes at plate boundaries. During the migration, seismic velocity and heterogeneous structures in its pathways may be temporarily perturbed, preferably triggering slow earthquakes. Here, we show that transient changes of seismic heterogeneity occurred 0-9 months before shallow slow earthquakes in the Nankai subduction zone, Japan, using very long-term (6-10 years) records of ambient seafloor noise. The heterogeneity changes preceding to shallow slow earthquakes were observed near the margin of the source region, while concurrent changes primarily occurred in the source region. We propose that the heterogeneity changes are attributed to dynamic fluid migration, and the difference in timings reflects the pore pressure level in the corresponding source region. When fluids are supplied to a source region under relatively low pressure, fluids are leaked out from its downdip or updip side, and slow earthquakes occur not immediately but with a time delay of at most 9 months. In the high pore pressure case, slow earthquakes occur immediately with fluid migration from the source region. This study suggests that the heterogeneous seismic structure is possibly changed by fluid migration before slow earthquakes in the Nankai subduction zone.

Research areas: Earthquakes
Data-Driven Two-Fault Modeling of the Mw 6.0 2008 Wells, Nevada (2021)

Structural fault complexity at depth affects seismic hazard, earthquake physics, and regional tectonic behavior, but constraining such complexity is challenging. We present earthquake source models of the February 21, 2008, Mw 6.0 Wells event that occurred in the Basin and Range in the western USA, suggesting the rupture of both the shallow and deep parts of a listric fault. We use a large data set including 150 local seismic waveforms from the USArray combined with high quality Interferometric Synthetic Aperture Radar and teleseismic waveforms. Rather than imposing an a priori fault geometry in the source inversions, as is often done in the literature, we use a data driven approach whereby all the faulting parameters and number of faults are determined by the data alone. We find a two fault normal faulting solution comprising: (i) a shallow (centroid depth ∼4.6 km) sub event with Mw 5.3 and fault dip of ∼77°; and (ii) a deeper (centroid depth ∼8.8 km), larger Mw 6.0 sub event on a fault with shallower dip angle (∼41°). Our preferred two fault model is consistent with aftershocks and with the tectonics of the region. The local USArray waveforms used in the modeling are key to detect the rupture of both shallow and deep parts of the possible listric fault. The lack of such dense and uniform coverage of earthquakes in other regions on Earth may explain why the full seismic rupture of listric faults may have gone undetected in the past. Thus, earthquake slip on whole listric faults may be more common than previously thought.

Research areas: Earthquakes
Dehydration of subducting slow-spread oceanic lithosphere in the Lesser Antilles (2017)

Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Fluid transport and release can be constrained with seismological data. Here we use joint active-source/local-earthquake seismic tomography to derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. We image the low P-wave velocity crustal layer on the slab top and show that it disappears beneath 60100 km depth, marking the depth of dehydration metamorphism and eclogitization. Clustering of seismicity at 120160 km depth suggests that the slabs mantle dehydrates beneath the volcanic arc, and may be the main source of fluids triggering arc magma generation. Lateral variations in seismic properties on the slab surface suggest that serpentinized peridotite exhumed in tectonized slow-spread crust near fracture zones may increase water transport to sub-arc depths. This results in heterogeneous water release and directly impacts earthquakes generation and mantle wedge dynamics.

Research areas: Earthquakes
Global occurrence and impact of small-to-medium magnitude earthquakes: a statistical analysis (2019)

Despite their much smaller individual contribution to the global counts of casualties and damage than their larger counterparts, earthquakes with moment magnitudes Mw in the range 4.05.5 may dominate seismic hazard and risk in areas of low overall seismicity, a statement that is particularly true for regions where anthropogenically-induced earthquakes are predominant. With the risk posed by these earthquakes causing increasing alarm in certain areas of the globe, it is of interest to determine what proportion of earthquakes in this magnitude range that occur sufficiently close to population or the built environment do actually result in damage and/or casualties. For this purpose, a global catalogue of potentially damaging eventsthat is, earthquakes deemed as potentially capable of causing damage or casualties based on a series of pre-defined criteriahas been generated and contrasted against a database of reportedly damaging small-to-medium earthquakes compiled in parallel to this work. This paper discusses the criteria and methodology followed to define such a set of potentially damaging events, from the issues inherent to earthquake catalogue compilation to the definition of criteria to establish how much potential exposure is sufficient to consider each earthquake a threat. The resulting statistics show that, on average, around 2% of all potentially-damaging shocks were actually reported as damaging, though the proportion varies significantly in time as a consequence of the impact of accessibility to data on damage and seismicity in general. Inspection of the years believed to be more complete suggests that a value of around 45% might be a more realistic figure.

Research areas: Earthquakes
Earthquake history of the Gokova fault zone by paleoseismologic trenching, SW Turkey (2022)

The Gulf of Gokova is a half-graben that is located on the southernmost part of the Aegean Extensional Region. The gulf is bounded on its north by the Gokova Fault Zone, which is an active fault zone that is composed of normal fault segments. We performed paleoseismological trenching throughout the fault zone at two sites, Keramos and Gereme sites. We have recognized two paleoearthquake horizons in Gereme trench and one paleoearthquake horizon in Keramos trench. Dating of samples by OSL and radiocarbon dating methods, and outcomes of Bayesian calculation in Oxcal, bracket the age of the older paleoevent as BCE 1099-161 and the younger event as CE 961-1574. Depending on the age bracket and written accounts in historical catalogues we compare the older paleoevent to the BCE 412-411 historical earthquake and the younger event to the CE 1493 historical earthquake. In conclusion, from this study, we have evidence for at least two surface faulting earthquakes during the Holocene, the most recent one representing the latest onshore surface rupturing event on the Gokova Fault Zone. Furthermore, depending on moment magnitude and rupture length relationships we suggest that the younger paleoearthquake event was about M = 7 according to a possible ~ 60-km-long surface rupture in at least between Kos island and Oren village.

Research areas: Earthquakes
Earthquake risk assessment for Tehran, Iran (2020)

The megacity of Tehran, the capital of Iran, is subjected to a high earthquake risk. Located at the central part of the AlpineHimalayan seismic belt, Tehran is surrounded by several active faults that show some M7+ historical earthquake records. The high seismic hazard in combination with a dense population distribution and several vulnerability factors mean Tehran is one of the top 20 worldwide megacities at a high earthquake risk. This article aims to prepare an assessment of the present-day earthquake risk in Tehran. First, the earthquake risk components including hazard, exposure, and vulnerability are evaluated based on some accessible GIS-based datasets (e.g., seismicity, geology, active faults, population distribution, land use, urban fabric, buildings height and occupancy, structure types, and ages, as well as the vicinity to some critical infrastructures). Then, earthquake hazard maps in terms of PGA are prepared using a probabilistic approach as well as a surface rupture width map. Exposure and vulnerability maps are also provided deterministically in terms of population density and hybrid physical vulnerability, respectively. Finally, all these components are combined in a spatial framework and an earthquake risk map is provided for Tehran.

Research areas: Earthquakes
The predictive relationship between earthquake intensity and tweets rate for real‐time ground‐motion estimation (2017)

The standard measure for evaluation of the immediate effects of an earthquake on people and manmade structures is intensity. Intensity estimates are widely used for emergency response, loss estimation, and distribution of public information after earthquake occurrence (Wood and Neumann, 1931; Brazee, 1976). Modern intensity assessment procedures process a variety of information sources. Those sources are primarily from two main categories: physical sensors (seismographs and accelerometers) and social sensors (witness reports). Acquiring new data sources in the second category can help to speed up the existing procedures for intensity calculations. One potentially important data source in this category is the widespread microblogging platform Twitter, ranked ninth worldwide as of January 2016 by number of active users, 320 million (Twitter, 2016). In our previous studies, empirical relationships between tweet rate and observed modified Mercalli intensity (MMI) were developed using data from the M 6.0 South Napa, California, earthquake (Napa earthquake) that occurred on 24 August 2014 (Kropivnitskaya et al., 2016). These relationships allow us to stream data from social sensors, supplementing data from other sensors to produce more accurate realtime intensity maps.In this study, we validate empirical relationships between tweet rate and observed MMI using new data sets from earthquakes that occurred in California, Japan, and Chile during MarchApril 2014. The statistical complexity of the validation test and calibration process is complicated by the fact that the Twitter data stream is limited for open public access, reducing the number of available tweets. In addition, in this analysis only spatially limited positive tweets (marked as a tweet about the earthquake) are incorporated into the analysis, further limiting the data set and restricting our study to a historical data set. In this work, the predictive relationship for California is recalibrated slightly, and a new set of relationships is estimated for Japan and Chile.

Research areas: Earthquakes
The lithospheric structure of the Gibraltar Arc System from wide‐angle seismic data (2020)

In continental settings, seismic failure is generally restricted to crustal depth. Crustal structure is therefore an important proxy to evaluate seismic hazard of continental fault systems. Here we present a seismic velocity model across the Gibraltar Arc System, from the Eurasian Betics Range (South Iberian margin), across offshore East Alboran and Pytheas (African margin) basins, and ending onshore in North Morocco. Our results reveal the nature and configuration of the crust supporting the coexistence of three different crustal domains: the continental crust of the Betics, the continental crust of the Pytheas Basin (south Alboran Basin) and onshore Morocco, and a distinct domain formed of magmatic arc crust under the East Alboran Basin. The magmatic arc under the East Alboran Basin is characterized by a velocity structure containing a relatively high-velocity lower crust (~7 km/s) bounded at the top and base by reflections. The lateral extension of this crust is mapped integrating a second perpendicular wide-angle seismic profile along the Eastern Alboran basin, together with basement samples, multibeam bathymetry, and a grid of deep-penetrating multichannel seismic profiles. The transition between crustal domains is currently unrelated to extensional and magmatic processes that formed the basin. The abrupt transition zones between the different crustal domains support that they are bounded by crustal-scale active fault systems that reactivate inherited structures. Seismicity in the area is constrained to upper-middle crust depths, and most earthquakes nucleate outside of the magmatic arc domain.

Research areas: Earthquakes