Angelyn W. Moore

The 2011 Magnitude 9.0 Tohoku-Oki Earthquake: Mosaicking the Megathrust from Seconds to Centuries

Detailed geophysical measurements reveal features of the 2011 Tohoku-Oki megathrust earthquake. Geophysical observations from the 2011 moment magnitude (Mw) 9.0 Tohoku-Oki, Japan earthquake allow exploration of a rare large event along a subduction megathrust. Models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places. Sources of high-frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip. Relative to the Mw 8.8 2010 Maule, Chile earthquake, the Tohoku-Oki earthquake was deficient in high-frequency seismic radiation—a difference that we attribute to its relatively shallow depth. Estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event.

Slip pulse and resonance of the Kathmandu basin during the 2015 Gorkha earthquake, Nepal

The bigger they are, the harder they fall The magnitude 7.8 Gorkha earthquake hit Nepal on 25 April 2015. The earthquake killed thousands and caused great damage. Galetzka et al. determined how the fault that caused this earthquake ruptured. The rupture showed a smooth slip pulse 20 km wide that moved eastward along the fault over about 6 s. The nature of the rupture limited damage to regular dwellings but generated shaking that collapsed taller structures. Science, this issue p. 1091 Continuous GPS and InSAR measurements record slip on the fault responsible for the 2015 Mw 7.8 Gorkha earthquake in Nepal. Detailed geodetic imaging of earthquake ruptures enhances our understanding of earthquake physics and associated ground shaking. The 25 April 2015 moment magnitude 7.8 earthquake in Gorkha, Nepal was the first large continental megathrust rupture to have occurred beneath a high-rate (5-hertz) Global Positioning System (GPS) network. We used GPS and interferometric synthetic aperture radar data to model the earthquake rupture as a slip pulse ~20 kilometers in width, ~6 seconds in duration, and with a peak sliding velocity of 1.1 meters per second, which propagated toward the Kathmandu basin at ~3.3 kilometers per second over ~140 kilometers. The smooth slip onset, indicating a large (~5-meter) slip-weakening distance, caused moderate ground shaking at high frequencies (>1 hertz; peak ground acceleration, ~16% of Earth’s gravity) and minimized damage to vernacular dwellings. Whole-basin resonance at a period of 4 to 5 seconds caused the collapse of tall structures, including cultural artifacts.

The Iquique earthquake sequence of April 2014: Bayesian modeling accounting for prediction uncertainty

The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. On 1 April 2014, this region was struck by a large earthquake following a two week long series of foreshocks. This study combines a wide range of observations, including geodetic, tsunami, and seismic data, to produce a reliable kinematic slip model of the Mw=8.1 main shock and a static slip model of the Mw=7.7 aftershock. We use a novel Bayesian modeling approach that accounts for uncertainty in the Greens functions, both static and dynamic, while avoiding nonphysical regularization. The results reveal a sharp slip zone, more compact than previously thought, located downdip of the foreshock sequence and updip of high-frequency sources inferred by back-projection analysis. Both the main shock and the Mw=7.7 aftershock did not rupture to the trench and left most of the seismic gap unbroken, leaving the possibility of a future large earthquake in the region.

National Weather Service Forecasters Use GPS Precipitable Water Vapor for Enhanced Situational Awareness during the Southern California Summer Monsoon

AbstractDuring the North American Monsoon, low-to-midlevel moisture is transported in surges from the Gulf of California and Eastern Pacific Ocean into Mexico and the American Southwest. As rising levels of precipitable water interact with the mountainous terrain, severe thunderstorms can develop, resulting in flash floods that threaten life and property. The rapid evolution of these storms, coupled with the relative lack of upper-air and surface weather observations in the region, make them difficult to predict and monitor, and guidance from numerical weather prediction models can vary greatly under these conditions. Precipitable water vapor (PW) estimates derived from continuously operating ground-based GPS receivers have been available for some time from NOAA’s GPS-Met program, but these observations have been of limited utility to operational forecasters in part due to poor spatial resolution. Under a NASA Advanced Information Systems Technology project, 37 real-time stations were added to NOAA’s GPS-...

Tropospheric correction for InSAR using interpolated ECMWF data and GPS Zenith Total Delay from the Southern California Integrated GPS Network

A tropospheric correction method for Interferometric Synthetic Aperture Radar (InSAR) was developed using profiles from the European Centre for Medium-Range Weather Forecasts (ECMWF) and Zenith Total Delay (ZTD) from the Global Positioning System (GPS). The ECMWF data were interpolated into a finer grid with the Stretched Boundary Layer Model (SBLM) using a Digital Elevation Model (DEM) with a horizontal resolution of 1 arcsecond. The output were converted into ZTD and combined with the GPS ZTD in order to achieve tropospheric correction maps utilizing both the high spatial resolution of the SBLM and the high accuracy of the GPS. These maps were evaluated for three InSAR images, with short temporal baselines (implying no surface deformation), from Envisat during 2006 on an area stretching northeast from the Los Angeles basin towards Death Valley. The RMS in the InSAR images was greatly reduced, up to 32%, when using the tropospheric corrections. Two of the residuals showed a constant gradient over the area, suggesting a remaining orbit error. This error was reduced by reprocessing the troposphere corrected InSAR images with the result of an overall RMS reduction of 15 – 68%.

The 2016 Kumamoto Mw = 7.0 Earthquake: A Significant Event in a Fault–Volcano System

The 2016 Kumamoto earthquake sequence occurred on the Futagawa–Hinagu fault zone near the Aso volcano on Kyushu island. The sequence was initiated with two major (M_w ≥ 6.0) foreshocks, and the mainshock (M_w = 7.0) occurred 25 h after the second major foreshock. We combine GPS, strong motion, synthetic aperture radar images, and surface offset data in a joint inversion to resolve the kinematic rupture process of the mainshock and coseismic displacement of the foreshocks. The joint inversion results reveal a unilateral rupture process for the mainshock involving sequential rupture of four major asperities. The slip area of the foreshocks and mainshock and the aftershock loci form a detailed complementary pattern. The mainshock rupture terminates near the rim of the caldera, leaving a ~10 km long gap of aftershocks. This area is characterized by high temperature and low shear wave velocity, density, and resistivity, which may be related to the partially melted geothermal condition. Ductile material property near the volcano may act as a “material barrier” to the dynamic rupture. Topographic weight of the caldera increases compressional normal stress on the fault plane, which may behave as a “stress barrier.” Long-term seismic hazard and deformation behaviors related to these two types of barriers are discussed in terms of the associated frictional mechanism. Significant postseismic creeps observed near the volcano area indicates a velocity strengthening frictional behavior near the rupture termination, which confirms that the “material barrier” mechanism is likely the dominant rupture termination mechanism.

Twenty-Two Years of Combined GPS Products for Geophysical Applications and a Decade of Seismogeodesy

Continuous GPS monitoring on global and regional scales has become an essential component of geophysical and meteorological infrastructure for studying fundamental Earth processes that drive natural hazards, weather, and climate. The NASA-funded “Solid Earth Science ESDR System (SESES)” project provides long-term Earth Science Data Records (ESDRs), the result of a combined solution of independent GPS analyses by the Jet Propulsion Laboratory and Scripps Institution of Oceanography using a common source of metadata archived at the Scripps Orbit and Permanent Array Center. The project has now produced up to twenty-two years of consistent, calibrated and validated ESDR products for over 3,200 GPS stations in western North America, other plate boundaries, and global networks. We describe the methodology to estimate a single set of time series with 24-h resolution of station displacements in north, east and vertical components. This is followed by a time series analysis for velocities, coseismic offsets, postseismic deformation, seasonal signals and nuisance offsets, primarily due to GPS antenna changes. Realistic one-sigma velocity are on the order of 0.03–0.05 mm/year in horizontal components and 0.1–0.3 mm/year in the vertical based on time series of 10–20 year duration. We present examples of time series that are well modeled by this parameterization and of time series that exhibit residual transient motions exhibiting episodic tremor and slip (ETS) processes. The project also catalogs seismic displacement and velocity waveforms estimated for a set of historical earthquakes in Japan and the U.S. through a seismogeodetic combination of GPS and collocated strong-motion accelerometers.

Tracking the weight of Hurricane Harvey’s stormwater using GPS data

GPS can track terrestrial water storage following extreme precipitation events, with potential to improve flood planning. On 26 August 2017, Hurricane Harvey struck the Gulf Coast as a category four cyclone depositing ~95 km3 of water, making it the wettest cyclone in U.S. history. Water left in Harvey’s wake should cause elastic loading and subsidence of Earth’s crust, and uplift as it drains into the ocean and evaporates. To track daily changes of transient water storage, we use Global Positioning System (GPS) measurements, finding a clear migration of subsidence (up to 21 mm) and horizontal motion (up to 4 mm) across the Gulf Coast, followed by gradual uplift over a 5-week period. Inversion of these data shows that a third of Harvey’s total stormwater was captured on land (25.7 ± 3.0 km3), indicating that the rest drained rapidly into the ocean at a rate of 8.2 km3/day, with the remaining stored water gradually lost over the following 5 weeks at ~1 km3/day, primarily by evapotranspiration. These results indicate that GPS networks can remotely track the spatial extent and daily evolution of terrestrial water storage following transient, extreme precipitation events, with implications for improving operational flood forecasts and understanding the response of drainage systems to large influxes of water.

Recent rapid disaster response products derived from COSMO-Skymed synthetic aperture radar data

The April 25, 2015 M7.8 Gorkha earthquake caused more than 8,000 fatalities and widespread building damage in central Nepal. Four days after the earthquake, the Italian Space Agencys (ASIs) COSMO-SkyMed Synthetic Aperture Radar (SAR) satellite acquired data over Kathmandu area. Nine days after the earthquake, the Japan Aerospace Exploration Agencys (JAXAs) ALOS-2 SAR satellite covered larger area. Using these radar observations, we rapidly produced damage proxy maps derived from temporal changes in Interferometric SAR (InSAR) coherence. These maps were qualitatively validated through comparison with independent damage analyses by National Geospatial-Intelligence Agency (NGA) and the UNITARs (United Nations Institute for Training and Researchs) Operational Satellite Applications Programme (UNOSAT), and based on our own visual inspection of DigitalGlobes WorldView optical pre- vs. post-event imagery. Our maps were quickly released to responding agencies and the public, and used for damage assessment, determining inspection/imaging priorities, and reconnaissance fieldwork.

Using ground-based GNSS observations to improve aviation turbulence monitoring and prediction

According to the U.S National Transportation Safety Board, atmospheric turbulence is the number-one cause of injuries to passengers and crew in nonfatal aviation accidents and is responsible for about 75 percent of all weather-related incidents and accidents each year. Significant improvements in discriminating and localizing turbulence events are required to meet the FAAs long-range Aviation Research Program objectives.