The pre-2004 9.0 Aceh earthquake Global Positioning System (GPS) velocity field along the western margin of the Sunda plate was dominated by the long-term secular velocity and elastic strain. Since then a sequence of the great earthquakes includes the 2005 8.6 Nias, 2007 8.5 Bengkulu, and 2012 8.6 and 8.2 Wharton Basin earthquakes, have occurred in different segments of the subduction zone and its vicinity, which resulted in significant coseismic and postseismic deformation on the Sunda plate. This study combined the published and the estimated GPS velocity fields between 1991–2016 from more than 150 GPS sites. These velocity fields are inverted to examine the angular velocities of the elastic crustal blocks and the variability of the coupling on the subduction trench. This analysis reveals the characteristic of the Sunda subduction interface over multiple earthquake cycles along different segments of the trench, whereby the subduction interface coupling coefficient changed both spatially and temporally after each rupture. The strongly coupled subduction interface along the plate convergence before 2004 earthquake is now partially coupled to freely slipping in the segments that ruptured during the 2005 and 2007 earthquakes, according to the present-day GPS velocity field (2012.2–2016.0). Interestingly, the best fitting model shows that the Siberut segment (0.5–2.0°S) remained fully coupled throughout the years. The result implies that the level of coupling along the highly segmented Sunda subduction interface varies over time, and that the great earthquake rupture was likely to be a result of the variation in the coupling.
The month-to-year-long deformation of the Earth’s crust where active subduction zones terminate is poorly explored. Here we report on a multidisciplinary dataset that captures the synergy of slow-slip events, earthquake swarms and fault-interactions during the ~5 years leading up to the 2018 M 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). It appears that this long-lasting preparatory phase initiated due to a slow-slip event that lasted ~4 months and released strain equivalent to a ~M 6.3 earthquake. We propose that the slow-slip event, which is the first to be reported in the HSS, tectonically destabilised the upper 20-40 km of the crust, producing alternating phases of seismic and aseismic deformation, including intense microseismicity (M<4) on neighbouring faults, earthquake swarms in the epicentral area of the M 6.9 earthquake ~1.5 years before the main event, another episode of slow-slip immediately preceding the mainshock and, eventually, the large (M6.9) Zakynthos Earthquake. Tectonic instability in the area is evidenced by a prolonged (~4 years) period of overall suppressed b-values (<1) and strong earthquake interactions on discrete strike-slip, thrust and normal faults. We propose that composite faulting patterns accompanied by alternating (seismic/aseismic) deformation styles may characterise multi-fault subduction-termination zones and may operate over a range of timescales (from individual earthquakes to millions of years).
On 11 January 2018 (18:26 UTC), a Mw 6.0 earthquake occurred approximately 30 km west of the Sagaing Fault in the Bago-Yoma Range (BYR). Using a local broadband seismic network and regional seismic stations, we refine the source parameters of the earthquake sequence. We relocate ~100 earthquake epicenters and determine the focal mechanism and centroid depth of the mainshock and 20 aftershocks with Mw>4. The relocated epicenters are distributed in an elongated zone oriented in a NW-SE direction that is consistent with the strike of the mainshock fault plane solution and the slip distribution derived from ALOS-2 InSAR observations. Most of the aftershocks have a pure thrust focal mechanism similar to the mainshock, except for four strike-slip aftershocks. The refined source parameters of the thrust events clearly delineate a fault dipping ~40˚ to the southwest at a depth range of 3-7 km, indicating that the earthquake sequence ruptured a previously unmapped, active fault. We interpret the earthquake sequence to be associated with pre-existing faults within the BYR anticlinorium. This earthquake sequence and historical seismicity indicate that the upper crust of the BYR is highly stressed, resulting in ongoing distributed deformation between the oblique Rakhine megathrust and the dextral Sagaing Fault. The seismic hazard posed by these active faults has been increasing with the development of infrastructure such as dams within the BYR. Our study highlights the need for high-resolution earthquake source parameter and strong ground motion attenuation studies for seismic hazard preparation and further understanding of the neotectonics of Myanmar.
We simulated tsunami propagation for several scenario slip distributions for the 1938 MW 8.3 earthquake along the Alaska Peninsula, and compared these to the observed records at Unalaska/Dutch Harbor and Sitka. The Sitka record is sensitive to the depth of slip but not the along-strike location, and is fit best by slip at shallow depth. The Unalaska record is sensitive mainly to the along-strike location of slip, and is fit best by slip that is concentrated in the eastern part of the presumed 1938 rupture zone. The tsunami data show that the actual 1938 earthquake rupture zone was smaller than previously thought, likely ~200 km in length, and had no slip near the Shumagin Islands or in the 2020 Simeonof earthquake’s rupture zone. The rupture models that best predict the 1938 tsunami lie within the region of high present day slip deficit inferred from GPS.
Using borehole strainmeters, we detected a 13-day long slow slip event on the Longitudinal Valley Fault, Taiwan. It is located between 8 to 15 km depth and has an equivalent moment magnitude of 5.5. The slow event has likely been promoted by the significant Coulomb stress changes (∼ + 1 MPa) imparted by a combination of coseismic and postseismic slip of the M w 6.8 Chengkung earthquake. Besides, insignificant coseismic slip is observed in the slow event region, suggesting that the latter could have acted as a barrier during the Chengkung earthquake. We also found a spatiotemporal correlation between the slow event and a cluster of repeating microearthquakes, suggesting aseismic slip as a possible driven mechanism of repeating ruptures. These results highlight the complex interplay between seismic and aseismic processes along the fault.
We use GPS observations to investigate the magnitude and spatial distribution of vertical coseismic and postseismic deformation of the Australian continent and compare these with elastic and viscoelastic model outputs. We observe and model surface deformation in Australia caused by six recent large far-field events: 2004 Mw 8.1 Macquarie Ridge, 2004 Mw 9.3 Sumatra-Anderman, 2005 Mw 8.6 in northern Sumatra, the 2007 series of Mw 8.5 and 7.9 in southern Sumatra, two events in 2012 of Mw 8.6 and 8.2 in northern Sumatra, and the 2009 Mw 7.8 south of New Zealand. Observed vertical coseismic deformation reaches 3 mm, with the magnitude varying spatially and by earthquake in broad agreement with modelling of coseismic deformation. Postseismic deformation is observed in all three coordinate components at Australian GPS sites nearest to these earthquakes, with deformations reaching several mm/yr in the vertical over multiple years. In particular, the Sumatran sequence produces observed subsidence in north-western Australia of up to 4 mm/yr over 2004.9-2010.0 where predictions based on one-dimensional viscoelastic Earth models replicate the subsidence but underpredict the vertical rate by a factor of two. Across all earthquakes, the models often fit one or two coordinate components of the observations, but rarely all three. Unmodeled lateral rheological structure likely contributes to this given the difference between the oceanic location of the earthquakes and the Australian continental setting of the GPS sites. The magnitude and spatial extent of these coseismic and postseismic deformations warrant their consideration in future updates of the geodetic terrestrial reference frame.
Coastal Louisiana is affected by sea level rates compounded by subsidence rates, leading to flooding and land loss. Subsidence in the region is caused by natural and anthropogenic processes that vary spatially and temporally across the Gulf of Mexico. Here, we quantify modern vertical and horizontal displacement using InSAR time-series and LiDAR differencing with data spanning between 1999-2020. Our study area is in Baton Rouge (BR), LA. It encompasses two Quaternary faults that cut cemented Pleistocene sediments. We test the ability of these methods to detect millimetric changes in an urban area with extraction and injection wells. Both methods indicate that the footwall of the BR fault has larger subsidence values (InSAR time series x̄=-0.552 to -0.732 mm/y) than the hanging wall of the fault (x̄=1.94 mm/y). LiDAR differencing accurately detects displacement trends, although it can overestimate the displacements. There are areas of uplift that spatially correlate to the locations of injection wells. Our results indicate that subsidence follows the spatial pattern of groundwater level changes proposed by previous studies, suggesting volumetric changes caused by fluid extraction and injection. The correlation of the BR fault zone with the boundary between blocks subsiding at different rates indicates that creep occurs along some sectors of the fault zone at rates of ~3 mm/y, similar to estimates from displaced structures. The creep may be accommodating changes in groundwater level rather than gravity and salt dynamics. The fault zones may be more permeable than surrounding areas, and more susceptible to hydrological and anthropogenic processes.
The electron content distribution of the north and south polar ionosphere is analyzed from 2001 to the beginning of 2019 from the Global Ionospheric Maps of VTEC computed each 15 minutes by UPC-IonSAT with a tomographic-Kriging combined technique. We have found the VTEC footprint of features previously reported by different authors and with different techniques: tongues of ionization, trough and dawn-side drifting structure, flux transfer event, Theta-aurora VTEC observation at SP, and Storm enhanced density (SED) during major geomagnetic storms. Moreover, by means of an unsupervised clustering algorithm (Learning Vector Quantization), we have characterized the main features of the ionospheric electron content climatology, separately for the north and south poles. In particular a mean Tongue Of Ionization (TOI) behaviour over south polar ionosphere during 1345UT-1945UT, from November to February, i.e. in local spring and summer seasons, is confirmed in agreement with recent findings.
The Lisbon Metropolitan Area (LMA, Portugal) has been affected by several destructive earthquakes nucleating both along the offshore Africa-Eurasia plate boundary and on onshore inherited intraplate faults. Using a dense GNSS dataset coupled with PSInSAR analysis, we provide new evidence of sinistral simple shear driven by a NNE-SSW first-order tectonic lineament. PSInSAR vertical velocities corroborate the GNSS strain-rate field, showing uplift/subsidence where the GNSS data indicate contraction/extension. We suggest the presence of a small block to the W of Lisbon moving independently towards the SW with a relative velocity of 0.96±0.20 mm/yr, whose boundaries are part of a complex and as yet poorly constrained strike-slip fault system, possibly rooting at depth into a simpler basement fault. Comparison between geodetic and seismic moment-rates indicates a high seismic coupling. We show that the contribution of intraplate faults to the seismic hazard in the LMA may be more important than currently assumed.
Taupo Volcano, located in the central part of the TVZ (Taupo volcanic Zone), North Island of New Zealand, is one of the most productive Rhyolitic centres in the world. Although its last eruption occurred about 1800 years ago, 16 periods of unrest have been identified including surface deformation, hydrothermal eruptions, and seismic swarms since 1870. The town of Taupo lies on the north-eastern shore of the lake filling the caldera of the volcano and is located close to recent seismic swarms and local surface deformation episodes highlighted in this report. The aim of this work is to study the different periods of episodic deformation, contrasting with the long-term deformation of the Taupo region, in order to constrain the sources generating local deformation. For this, an analysis of GPS (continuous and campaign stations) and InSAR data (from two satellites, EnviSAT and ALOS) was conducted. After correcting the data for several external factors such as subsidence generated by water pumping in the Wairakei-Tauhara geothermal station and displacements associated with slow slip events along the Hikurangi subduction interface, periods of local deformation have been identified. We highlight two periods of uplift with rates of 10 mm/yr in 2004-2008 and in 2011-2013 accompanied by more or less rapid horizontal deformation punctuated by seismic swarms. The geodetic data were inverted to characterize the deformation sources using the GBIS software, allowing the use of different analytical models. In order to explain the different periods of deformation over time, at least three sources at different locations are needed, revealing the presence of different processes at depths ranging from ∼ 10 km to ∼ 0.5 km and whose causes can vary given the complexity of the tectonic context characterizing the region.
Earthquake-triggered slow-moving landslides are not well studied mainly due to lack of high-resolution in-situ geodetic observations both in time and space. Satellite-based interferometric synthetic aperture radar (InSAR) has shown potential in landslides applications, however, it is challenging to detect earthquake-triggered slow-moving landslides over large areas due to the effects of post-seismic tectonic deformations, atmospheric delays, and other spatially propagated errors (e.g., decorrelation noises caused unwrapped errors). Here, we present a novel InSAR phase-gradient-based time-series approach to detect slow-moving landslides that triggered by the 2016 Mw 7.8 Kaikōura earthquake. 21 earthquake-triggered large (> 0.1 km 2) slow-moving landslides are detected and studied. Our results reveal decaying characteristics of the temporal evolutions of these landslides, that averagely after 3.9 years since the earthquake, their postseismic velocity will decay 90% and close to pre-seismic level. Our study opens new perspectives for the research of the mass balance of earthquakes and helps reduce associated hazards.
We investigate 85 129 MODIS satellite active fire events from 2007 to 2015 in the Niger Delta of Nigeria. The region is the oil base for Nigerian economy and the hub of oil exploration where oil facilities (i.e. flowlines, flow stations, trunklines, oil wells and oil fields) are domiciled, and from where crude oil and refined products are transported to different Nigerian locations through a network of pipeline systems. Pipeline and other oil facilities are consistently susceptible to oil leaks due to operational or maintenance error, and by acts of deliberate sabotage of the pipeline equipment which often result in explosions and fire outbreaks. We used ground oil spill reports obtained from the National Oil Spill Detection and Response Agency (NOSDRA) database (see www.oilspillmonitor.ng) to validate MODIS satellite data. NOSDRA database shows an estimate of 10 000 spill events from 2007 - 2015. The spill events were filtered to include largest spills by volume and events occurring only in the Niger Delta (i.e. 386 spills). By projecting both MODIS fire and spill as ‘input vector’ layers with ‘Points’ geometry, and the Nigerian pipeline networks as ‘from vector’ layers with ‘LineString’ geometry in a geographical information system, we extracted the nearest MODIS events (i.e. 2192) closed to the pipelines by 1000m distance in spatial vector analysis. The extraction process that defined the nearest distance to the pipelines is based on the global practices of the Right of Way (ROW) in pipeline management that earmarked 30m strip of land to the pipeline. The KML files of the extracted fires in a Google map validated their source origin to be from oil facilities. Land cover mapping confirmed fire anomalies. The aim of the study is to propose a near-real-time monitoring of spill events along pipeline routes using 250 m spatial resolution of MODIS active fire detection sensor when such spills are accompanied by fire events in the study location.
Great Salt Lake (GSL), Utah, lost 1.89 +/- 0.04 meters of water during the 2012 to 2016 drought. During this timeframe, data from the GRACE mission do not detect anomalous mass loss, but nearby Global Positioning System (GPS) stations show significant shifts in position. We find that crustal deformation, from unloading the Earth’s crust with the observed GSL water loss alone, does not explain the GPS displacements, suggesting contributions from additional water storage loss surrounding GSL. This study applies a damped least squares inversion to the 3D GPS displacements to test a range of distributions of radial mass load rings to fit the observations. When considering the horizontal and vertical displacements simultaneously, we find the most realistic distribution of water loss while also resolving the observed water loss of the lake. Our preferred model identifies radially decreasing mass loss up to 64 km from the lake. The contribution of exterior groundwater loss is substantial (10.9 +/- 2.8 km^3 vs. 5.5 +/- 1.0 km^3 on the lake), and greatly improves the fit to the observations. Nearby groundwater wells exhibit significant water loss during the drought, which substantiates the presence of significant water loss outside of the lake, but also highlights greater spatial variation than our model can resolve. We observe seismicity modulation within the inferred load region, while the region outside the (un)loading reveals no significant modulation. Drier periods exhibit higher quantities of events than wetter periods and changes in trend of the earthquake rate are correlated with regional mass trends.
We propose a method for Global Ionospheric Maps of Total Electron Content forecasting using the Nearest Neighbour method. The assumption is that in a database of global ionosphere maps spanning more than two solar cycles, one can select a set of past observations that have similar geomagnetic conditions to those of the current map. The assumption is that the current ionospheric condition can be expressed by a linear combination of conditions seen in the past. The average these maps leads to common geomagnetic components being preserved and those not shared by several maps being reduced. The method is based on searching the historical database for the dates of the maps closest to the current map and using as a prediction the maps in the database that correspond to time shifts on the prediction horizons. In contrast to other methods of machine learning, the implementation only requires a distance computation and does not need a previous step of model training and adjustment for each prediction horizon. Also provides confidence intervals for the forecast. The method has been analyzed for two full years (2015 and 2018), for selected days of 2015 and 2018, i.e., two storm days and two non-storm days and the performance of the system has been compared with CODE (24- and 48-hour forecast horizons).
The 25-27 August geomagnetic storm was the third largest storm in 24th solar cycle, which was a surprising space event that generated in the background of very low solar activity. This study presents an overview of temporal-spatial behaviors of ionospheric plasma irregularities as functions of geographic longitude, latitude and altitude by ground-based (GNSS receivers and ionosonde) instruments and space-borne (Swarm-A and Swarm-B) satellites. The results not only reveal the enhanced equatorial ionization anomaly (EIA) and hemispheric asymmetry over the Asian-Australian and American sectors in a particular time, but also discover the development of hemispheric asymmetric features of global ROTI in the main and recovery phases. In addition, this storm also triggered positive plasma irregularities in altitudes of 100 to 150km near Auroral zone, and the changed ratio of bottom-side plasma irregularities exceeded 250%, which has been cross validated by multiple instrument and TIE-GCM’s simulation. Furthermore, the thermospheric density ratio O/N2, equatorial electrojet and vertical E×B drifts suffered from the storm largely, the equatorial and mid-latitude plasma irregularities may be a combined action of thermospheric composition change, equatorial electrojet and vertical E×B drifts. Finally, the storm also induced positive Joule heating irregularities in Auroral ionosphere in altitudes of 100 to 400km with a maximum changed ratio of >200%, as well as the cross Polar voltage enhanced to ~90kv. The Polar ionospheric irregularities may be associated with the additional energy input through the ways of particle precipitation, Joule heating and ionospheric currents intensification.
The Delaware Basin, Texas is currently a hot-spot of induced seismicity and ground deformation due to fluid extraction and injection associated with horizontal drilling techniques; however, the driving mechanism behind the seismicity and deformation remains under debate. Using vertical and east-west horizontal surface deformation measurements derived from Sentinel-1 InSAR, we show that the subsurface responds differently to oil and gas activity in the northern and southeastern portions of the basin. In the north, where there is little seismicity, deformation patterns display long-wavelengths and equidimensional patterns. In contrast, the southeast region hosts most of the seismicity and displays spatial deformation patterns with narrow linear features that strike parallel to the maximum principal horizontal stress and to trends in seismicity, suggesting movement along normal faults. We model a linear deformation feature using edge dislocations and show that the InSAR observations can be reproduced by slip on normal faults contained within the Delaware Mountain Group (DMG), the formation that hosts local wastewater injection and the majority of earthquakes. Our model consists of three parallel, high-angle normal faults, with two dipping toward one another in a graben structure. Slip magnitudes reach up to 27.5 cm and are spatially correlated with injection wells. Measured seismicity can only explain ~2% of the fault motion predicted by our fault model, suggesting that slip leading to the deformation is predominantly aseismic. We conclude that seismic and aseismic fault motion in the southeastern Delaware Basin is likely driven by wastewater injection near critically-stressed normal faults within the DMG.
Orbit determination of probes orbiting Solar System bodies is currently the main source of our knowledge about their internal structure, inferred from the estimate of their gravity field and rotational state. Non-gravitational forces acting on the spacecraft need to be accurately included in the dynamical modeling (either explicitly or in the form of empirical parameters) to not degrade the solution and its geophysical interpretation. In this work, we present our recovery of NASA GRAIL orbits and our lunar gravity field solutions up to degree and order 350. We propose a systematic approach to select an optimal parametrization with empirical accelerations and pseudo-stochastic pulses, by checking their impact against orbit overlaps or, in the case of GRAIL, the very precise inter-satellite link. We discuss how parametrization choices may differ depending on whether the goal is limited to orbit reconstruction or if it also includes the solution of gravity field coefficients. We validate our setup for planetary geodesy by iterating extended lunar gravity field solutions from pre-GRAIL gravity fields, and we discuss the impact of empirical parametrization on the interpretation of gravity solutions and of their error bars.
Viscoelastic processes in the upper mantle redistribute seismically generated stresses and modulate crustal deformation throughout the earthquake cycle. Geodetic observations of these motions at the Earth’s surface offer the possibility of constraining the rheology of the upper mantle. Parsimonious representations of viscoelastically modulated deformation should simultaneously be able to explain geodetic observations of rapid postseismic deformation and near-fault strain localization late in the earthquake cycle. We compare predictions from time-dependent forward models of deformation over the entire earthquake cycle on and surrounding an idealized vertical strike-slip fault in a homogeneous elastic crust underlain by a homogeneous viscoelastic upper mantle. We explore three different rheologies as inferred from laboratory experiments: 1) linear-Maxwell, 2) linear-Burgers, 3) power-law. Both the linear Burgers and power-law rheological models can be made consistent with fast and slow deformation phenomenology from across the entire earthquake cycle, while the single-layer linear Maxwell model cannot. The kinematic similarity of linear Burgers and power-law models suggests that geodetic observations alone are insufficient to distinguish between them, but indicate that one may serve as a proxy for the other. However, the power-law rheology model displays a postseismic response that is strongly earthquake magnitude dependent, which may offer a partial explanation for observations of limited postseismic deformation near magnitude 6.5-7.0 earthquakes. We discuss the role of mechanical coupling between frictional slip and viscous creep in controlling the time-dependence of regional stress transfer following large earthquakes and how this may affect the seismic hazard and risk to communities living close to fault networks.