S. E. Owen

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.

Effects of Nonplanar Fault Topology and Mechanical Interaction on Fault-Slip Distributions in the Ventura Basin, California

To assess the control of fault geometry and mechanical interactions on fault-slip distributions in a complex natural system, we present results from three- dimensional mechanical models incorporating both nonplanar and rectangular planar representations of active faults within the Ventura basin region of southern California. We find that the incorporation of geologically constrained nonplanar fault surfaces into numerical models of active deformation results in a better match to available geologic slip-rate data than models utilizing rectangular planar fault surfaces. The model results demonstrate that nonplanar fault geometry and mechanical interactions exert a strong control on resultant slip distributions. Additionally, we find that slip rates at most locations along the surface trace of Ventura faults are not likely to rep- resent average values for the entire fault surface. We propose that results from three- dimensional mechanical models using realistic (i.e., nonplanar) fault geometry can be used to both predict slip rates at specific locations and determine whether existing site- specific slip-rate estimates are representative of average fault-slip rates. Although geo- metric irregularities along-fault surfaces should resist slip, planar faults can have lesser slip than nonplanar faults due to the differing mechanical interactions among nearby faults in the two representations. This suggests that models using simplified or planar fault geometry are likely to inaccurately simulate regional deformation. We assert that detailed knowledge of three-dimensional fault shape as well as the geometry and con- figuration of deep fault intersections is essential for accurate seismic hazard char- acterization of regions of complex faulting such as the Ventura basin of southern California.

Crowdsourced earthquake early warning

Consumer devices and real and simulated earthquake data demonstrate that earthquake early warning can be achieved via crowdsourcing. Earthquake early warning (EEW) can reduce harm to people and infrastructure from earthquakes and tsunamis, but it has not been implemented in most high earthquake-risk regions because of prohibitive cost. Common consumer devices such as smartphones contain low-cost versions of the sensors used in EEW. Although less accurate than scientific-grade instruments, these sensors are globally ubiquitous. Through controlled tests of consumer devices, simulation of an Mw (moment magnitude) 7 earthquake on California’s Hayward fault, and real data from the Mw 9 Tohoku-oki earthquake, we demonstrate that EEW could be achieved via crowdsourcing.

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.

Rapid Damage Mapping for the 2015 Mw 7.8 Gorkha Earthquake Using Synthetic Aperture Radar Data from COSMO–SkyMed and ALOS-2 Satellites

The 25 April 2015 M_w 7.8 Gorkha earthquake caused more than 8000 fatalities and widespread building damage in central Nepal. The Italian Space Agency’s COSMO–SkyMed Synthetic Aperture Radar (SAR) satellite acquired data over Kathmandu area four days after the earthquake and the Japan Aerospace Exploration Agency’s Advanced Land Observing Satellite-2 SAR satellite for larger area nine days after the mainshock. We used these radar observations and rapidly produced damage proxy maps (DPMs) derived from temporal changes in Interferometric SAR coherence. Our DPMs were qualitatively validated through comparison with independent damage analyses by the National Geospatial-Intelligence Agency and the United Nations Institute for Training and Research’s United Nations Operational Satellite Applications Programme, and based on our own visual inspection of DigitalGlobe’s WorldView optical pre- versus postevent imagery. Our maps were quickly released to responding agencies and the public, and used for damage assessment, determining inspection/imaging priorities, and reconnaissance fieldwork.

Open access to geophysical data sets requires community responsibility

In our increasingly digital age, access to data is becoming faster and easier. This has many positive consequences for scientific discovery, but it also presents challenges for protecting the data collectors and ensuring proper citation (e.g., M. A. Parsons et al.,Eos, 91(34), 297, doi:10.1029/2010EO340001). These issues have been concerns of UNAVCOs staff and those involved in the governance of UNAVCO as they crafted a new open data policy that became effective on 2 March 2012. UNAVCO is a nonprofit consortium of 177 university and research institutions from around the world. Founded in 1984 as the University Navstar Consortium and formally incorporated in 2001 as UNAVCO, Inc., the organization facilitates the collection and archiving of geodetic data (http://www.unavco.org).

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.

System-on-Chip Architecture Design for Intelligent Sensor Networks

While wireless sensor networks can generically be used for a wide variety of applications, breakthrough innovations are most often achieved when driven by a genuine need or application, with its specific system-level and science-related requirements and objectives. Hence, our work focuses on the development of wireless sensor network system-on-chip devices and supporting software for volcano monitoring, which we call Sensor Network for Active Volcanoes (SNAV). In this paper we present preliminary results of our research and development work on intelligent sensor networks for monitoring hazardous environments especially the SNAV system-on-chip design for active volcanoes monitoring.

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.