Plenary Session II

Basics of GNSS Positioning, and How that Shapes the GNSS Contribution to Tsunami Early Warning
Jeff FreymuullerUniversity of Alaska, Fairbanks
  Earthquake ground motions measured by GNSS can provide a powerful augmentation to tsunami early warning systems. The basic design of a GNSS tsunami early warning system is shaped by the characteristics of the GNSS signal structure and signal propagation delays, and by the process of inverting observed ground motions to determine slip on the causative fault. Data processing techniques to derive position and/or velocity time series from streams of GNSS data are, at the core, about calibrating or estimating path delays and nuisance parameters so that observed changes in the phase of GNSS signals can be converted into estimates of position or velocity changes. Different approaches lead to different output data products. In this talk, I will summarize the basics of GNSS as they are relevant to this problem, and the output data streams that result. I will finish by illustrating how the GNSS derived ground motions constrain basic properties of the earthquake source; quantitative modeling of the ground motions will be presented in the following talk

How the Real-Time GNSS Can Contribute to Tsunami Early Warning in Association with Other Geophysical Measurements
Yusaku OhtaTohoku University
  The real-time GNSS have an advantage in the robust estimation of the coseismic fault dimensions and location because the spatial pattern of permanent coseismic displacement from the GNSS measurement is strongly affected by these source parameters. The use of onshore GNSS data alone, however, has limitations with regard to precise tsunami warnings because huge interplate earthquakes occur far offshore. Tsunami forecasting based on the estimated earthquake size and its expansion determined by using onshore data is also an indirect estimation and thus it is expected that the combined use of both onshore and offshore data will provide more reliable near field tsunami forecasting. In this talk, I will summarize the possibility of combination use of real-time GNSS and other geophysical measurement such as the offshore tsunami data based on the recent Japanese dense real-time on- and offshore network environment. 

Plenary Session III A- Seismic Sources

Spontaneous Rupture Simulations of Large Earthquakes for Tsunami  Early Warning System
Eiichi Fukuyama and Tatsuhiko Saito, National Research Institute for Earth Science and Disaster Resilience
  A strategy for the preparation of scenario of the tsunami generation source will be discussed. One of the possible inputs could be source  models computed based on spontaneous dynamic rupture simulation of earthquakes, which are hopefully similar to future large earthquakes.  Using the simulated source model, synthetic tsunami waveforms could  be computed, which will be a virtual input data to validate the real-time  tsunami early warning system.

Tsunami Squares Approach to Water Wave Generation and Propagation
Steven Ward, Institute of Geophysics and Planetary Physics, University of California, Santa Cruz
“Tsunami Squares” (TS) is an intuitive and nearly equation-free approach to simulate a wide range of flow scenarios including tsunami, landslides, lavas, glacier movement, storm surge, and sediment transport.  All of these scenarios operate basically the same way -  a set of accelerations (gravity, wind, various frictions) drives a motion constrained by conservation of mass and linear momentum. TS supposes to know the thickness, velocity, and acceleration of material in a fixed filled grid of squares at time t. Now, imagine a second empty grid of squares coinciding with the filled grid. Over time increment dt, each square in the filled grid moves a distance and direction dictated by its velocity and acceleration. The mass and linear momentum of the transported material is then partitioned into at most four cells of the empty grid. After each square in the filled grid has been moved, the total mass and linear momentum of material is summed for each cell in the initially empty grid. (Dividing the latter by the former gives the mean velocity). The second empty grid now becomes the fixed, filled grid where we know the thickness and velocity of the material at time t+dt.  Accelerations from gravity, wind, and various frictions are then computed by whatever laws govern the material and the process repeated.  I show several examples of earthquake and landslide tsunami in the talk. 
  Please visit my web site  and YouTube Channel for a preview of many other TS applications.

Spatial GNSS/DART Requirements for Real-time Local Tsunami Warning Using Joint Source Inversions
Amy L. Williamson and Andrew V. NewmanSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology
  While Deep-Ocean Assessment and Reporting of Tsunami (DART) gauges record the seaward passing waves, Global Navigational Satellite Systems (GNSS) record the abrupt movements on the landward side of major subduction zone earthquakes.  With careful placement, the next generation of DART gauges can increase the temporal window for tsunami early warning at localities near the source regions.  Likewise, high-rate continuous GNSS sites near coasts can work in concert to provide rapid joint assessments of an earthquake’s tsunami potential [e.g. Williamson et al., JGR, 2017]. Given some base assumptions about tsunami generation dominated along the near-trench environment, we develop a global analysis of subduction zones to evaluate their real-time viability for joint-inversion of land-GNSS and DART data. While this work is ongoing, we will show both regional focus study results in Cascadia and Japan, as well as preliminary global results that give minimum warning times one could expect in certain environments. Likewise, we will highlight zones for which there just does not exist sufficient land to reliably resolve the near-trench tsunami potential--a particular concern for devastating, but poorly understood tsunami earthquakes.  Such environments would be particularly well suited for seafloor geodetic tools that could relay real-time deformation information. 

Plenary Session III B- Tsunami Source Modeling and Requirements

Rapid Tsunami Inundation and Damage Forecasting with Precise Tsunami Source Model with GNSS data
Shunichi Koshimura, Tohoku University
  This talk focuses on recent advances of real-time tsunami inundation and damage forecasting system that will be lunched in November 2017 as a function of the central government's disaster response system. The system consists of precise tsunami source modeling with GNSS data, acceleration of  propagation and inundation simulation on high performance computing infrastructure, and a mapping system. The results are disseminated as mapping products to responders of the central government to be utilized for their emergency/response activities, e.g. identifying the number of exposed population, and potential damage to houses and critical infrastructures.

Connecting Earthquake Source Models to Tsunami Forecasts
Diego MelgarUniversity of California, Berkeley
  For the problem of near-field tsunami warning, earthquake source models by themselves provide only limited actionable information. In this talk, I will discuss strategies to connect these models to rapid forecasts of expected tsunami intensity. I will survey and synthesize recent results from the hazards community to address two important questions, how good can the forecasts be? And, how fast, after rupture nucleation, can we reasonably expect them? Finally, I will also discuss the salient research problems in this field and potential strategies to address them.

GPS-Aided Tsunami Early detection System (GATES)—Tsunami Source Modeling and Requirements
Y. Tony Song, Kejie Chen, Zhen Liu, Yoaz Bar-Sever, and Robert Khachikyan, NASA Jet Propulsion Laboratory, California Institute of Technology
 Much progress has been made in demonstrating GNSS augmentation for tsunami early warning. However, most of the demonstrations were carried out after the event. Here we report progress in developing a real-time GPS-Aided Tsunami Early detection System (GATES). Since the system was automated in 2015, we have tested over 30 large (> M6.5) earthquakes, including the 2015 M7.7 Nepal earthquake, the 2015 M8.3 Illapel earthquake, and the 2016 M7.8 New Zealand earthquake. Our validation approach is based on comparing the real-time performance with after-event processed data. We have focused on testing the GATES system in determining earthquake source and tsunami scales with a timely, accurate, reliable, and effective manner. The ultimate performance for the GATES system is measured by the two key metrics: the time used to derive the tsunami scale, and the accuracy of the tsunami scale in quantifying tsunami heights at the point of interest. The testing results and statistics will be presented.
  In addition, we have also investigated the reliability and effectiveness of using GNSS for tsunami detection. The major problem is the limited coverage and sparse distribution of real-time GNSS observations along the global coast. To overcome the limitations, a novel strategy by using both seismic and GNSS measurements has been proposed and is under-developing. Preliminary results will be reported.  

Plenary Session IV - Ionospheric Remote Sensing

Advances in Understanding Natural-Hazards-Generated TEC Perturbations Using Ground-Based and Spaceborne Measurements
Attila Komjathy1, Giorgio Savastano1,2, Xing Meng1, Olga Verkhoglyadova1, Anthony Mannucci1
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 2University of Rome “La Sapienza,” Rome, Italy
  Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcanic eruptions, and tsunamis.
  We will show examples for early detection of natural hazards generated ionospheric signatures using ground-based and space-borne GPS receivers. We will discuss recent results from the U.S. Real-time Earthquake Analysis for Disaster Mitigation Network (READI). By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage. It is also expected that ionospheric monitoring of TEC perturbations might become an integral part of existing natural hazards warning systems.

From Sumatra 2004 to Chile 2015 (through the revolutionary observations of Tohoku-Oki 2011): What We learned about Tsunami Detection by Ionospheric Sounding 
Giovanni Occhipinti, Institut de Physique du Globe de Paris, Paris, France; Lucie Rolland (Géoazur), Shingo Watada (ERI), Jonathan Makela (Univ. Illinois), Aurélien Bablet (IPGP), Florent Aden-Antoniow (IPGP), Pierdavide Coisson (IPGP), Philippe Lognonné (IPGP), Elvira Astafyeva (IPGP), Helene Hebert (CEA)
  The tsunamigenic Tohoku-Oki earthquake (2011) strongly affirms, again, after the 26 December 2004 Sumatra earthquake, the necessity to open new paradigms in oceanic monitoring. Detection of ionospheric anomalies following the Sumatra earthquake tsunami (e.g., Occhipinti et al. 2006) demonstrated that the ionosphere is sensitive to earthquake and tsunami propagation; ground and oceanic vertical displacement induces acoustic-gravity waves propagating within the neutral atmosphere that are detectable in the ionosphere. Observations supported by modeling proved that tsunamigenic ionospheric anomalies are deterministic and reproducible by numerical modeling via the ocean/neutral-atmosphere/ionosphere coupling mechanism (Occhipinti et al., 2008). To prove that the tsunami signature in the ionosphere is routinely detected, we show here perturbations of total electron content (TEC) measured by GPS following tsunamigenic eartquakes from 2004 to 2011 (Rolland et al., 2010, Occhipinti et al., 2013), nominally, the Sumatra (26 December 2004 and 12 September 2007), Chile (14 November 2007), Samoa (29 September 2009) and the recent Tohoku-Oki (11 March 2011). Based on the observations close to the epicenter, mainly performed by GPS networks located in Sumatra, Chile and Japan, we highlight the TEC perturbation observed within the first hour after the seismic rupture. This perturbation contains information about the ground displacement, as well as the consequent sea surface displacement resulting in the tsunami. In addition to GPS/TEC observations close to the epicenter measured by GEONET network, new exciting measurements in the far-field were performed by Airglow measurement in Hawaii; those measurements show the propagation of the IGWs induced by the Tohoku tsunami in the Pacific Ocean (Occhipinti et al., 2011). This revolutionary imaging technique is today supported by two new observations of moderate tsunamis: Queen Charlotte (M: 7.7, 27 October 2013) and Chile (M: 8.2, 16 September 2015). The potential idea to put an Airglow camera on a satellite opens new exciting perspectives for tsunami detection.
  In this talk we present all this new tsunami observations in the ionosphere and we discuss, under the light of modeling, the potential role of ionospheric sounding in the oceanic monitoring and future tsunami warning system by GPS, Airglow and OTH radar (Coisson et al., 2011).
  The review presented in this talk is published by AGU as “The Seismology of Planet Mongo: the 2015 Ionospheric Seismology Review” (Occhipinti, 2015). 
  All ref. here @

Real-Time Detection of Tsunami Ionospheric Disturbances with Stand-Alone GNSS Receivers: A Prototype Implementation in the JPL’s GDGPS System
Giorgio Savastano1,2, Attila Komjathy2, Olga Verkhoglyadova2, Yoaz Bar-Sever2, Anthony J.Mannucci2, Yong Wei3,4, Augusto Mazzoni1 and Mattia Crespi1
1University of Rome, 2 Jet Propulsion Laboratory, Pasadena, California, 3 National Oceanic & Atmospheric Administration, Seattle, Washington, 4 Joint Institute for the Study of Atmosphere and Ocean (JISAO), University of Washington, Seattle, Washington
  Tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances are studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, also known as VARION (Variometric Approach for Real-Time Ionosphere Observation), and for the first time, we estimate slant TEC (sTEC) variations in a real-time scenario from GPS and Galileo constellations. The efficiency of the real-time sTEC estimation using the VARION algorithm has been demonstrated for the 2012 Haida Gwaii tsunami event. We present two real-time strategies for tsunami ionospheric disturbances detection using GNSS ionospheric observations. We are implementing the VARION algorithm in the JPL’s GDGPS system which provide access to a global network of continuously operative GNSS stations. We conclude that the integration of different satellite constellations is a crucial step forward to increasing the reliability of real-time tsunami detection systems using ground-based GNSS receivers as an augmentation to existing tsunami early warning systems.

Plenary Session V - Data Processing

Real-time High-Rate Multi-GNSS and its Noise Characteristics for Tsunami Early Warning over Asia-Pacific Regions
Jianghui Geng, Shaoming Xin, Yuanxin Pan, Jiang Guo
GNSS Research Center , Wuhan University
  Real-time GNSS precise point positioning (PPP) is capable of measuring centimeter-level positions epoch by epoch at a single station, and is thus treasured in tsunami/earthquake early warning where static displacements in the near field are critical to rapidly and reliably determining the magnitude of destructive events. However, most operational real-time PPP systems at present rely on only GPS data. Such systems are insufficienct since  the availability and high reliability of precise displacements cannot be maintained continuously in real time. This is a crucial requirement for disaster resistance and response. Multi-GNSS, including GLONASS, BeiDou, Galileo and QZSS, can solve this problem since more satellites per epoch (e.g. 30-40) will be available. In this case, positioning failure due to data loss or blunders can be minimized, and on the other hand, positioning initializations can be accelerated to a great extent since the satellite geometry for each epoch will be enhanced enormously. This in turn will greatly improve the success rate of ambiguity fixing, which can play a critical role as an indicator, and as a means to guarantee success in achieving measurements of centimeter-level ground displacements. We established a prototype real-time multi-GNSS PPP service based on Australian national network which can collect and stream high-rate data from all five navigation systems. We estimated high-rate satellite clock corrections and enabled undifferenced ambiguity fixing for multi-GNSS, which therefore ensures high availability and reliability of precise displacement estimates in contrast to GPS-only systems. We will report the preliminary performance of this service and analyze its potential to tsunami early warning for Asia-Pacific regions.

Global Seismic Monitoring with Real-Time GPS
Tim MelbourneCentral Washington U.
  Real-time GPS is a disruptive technology whose ongoing proliferation has transformed all aspects of precise timing and navigation. Upwards of a thousand real-time stations operate throughout the Cascadia and San Andreas systems and are useful for seismic and tsunami monitoring as well as a host of other natural hazards mitigation applications; thousands more operate throughout the circum-Pacific.  I will discuss CWU’s development of a comprehensive seismic monitoring system for the western US based on real-time GPS, its interface to traditional seismic monitoring, and its ongoing expansion into a global system that utilizes the increasingly dense international station distribution. 

Plenary Session VI - GNSS Networks

Elisabetta D’Anastasio

GNSS data sharing in the Asia Pacific region: a governmental perspective on progress and challenges
John Dawson, Geoscience Australia and Chair Geodesy Working Group of the United Nations Global Geospatial Information Management for Asia and the Pacific (UN-GGIM-AP)
  This presentation will review progress towards providing open access to real-time GNSS networks in the Asia-Pacific operated by government agencies. The efforts of the UN-GGIM community through United Nations process will be summarized. Successes including the Asia Pacific Reference Frame (APREF) initiative will be reviewed while ongoing challenges will be highlighted.

UNAVCO Operated GNSS Networks and Real-Time Data Delivery
David A. Phillips, Christian Walls, Glen Mattioli, David Mencin, Kathleen Hodgkinson, Charles Meertens, Frederick Blume, Henry Berglund, Otina Fox, Karl Feaux, Charles Sievers, UNAVCO
  The U.S. National Science Foundation (NSF) funded GAGE Facility, managed by UNAVCO, operates ~1300 continuous GNSS stations distributed across North America, northern South America, and spanning the circum-Caribbean with nearly 800 stations streaming GNSS-GPS data in real-time.  Data and derived products from all stations are freely available.  UNAVCO has embarked on significant improvements to the original infrastructure and scope of our networks based upon feedback from and in partnership with stakeholders to enable enhancement of  earthquake early warning, tsunami early warning, and tropospheric modeling.  We anticipate that the Plate Boundary Observatory (PBO) and related networks will form a backbone for these emerging applications with high quality, low latency raw and processed GNSS data as well as providing a platform for integration with other sensors, including broadband and strong motion seismometers.  We present the infrastructure and data management requirements for providing high quality low latency GNSS data as well as the planned future state of these networks as an international resource.

Seismogeodesy Applied to Large Earthquake Characterization in Chile
Sebastian Riquelme, National Seismological Center, University of Chile
  Recent efforts have been made to characterize large earthquakes in real time in Chile. In the last seven years Chile has been struck with 3 large earthquakes (Mw > 8). After the devastating Maule Earthquake, the National Seismological Center started to operate with the aim of monitoring real time events, passing from being an academic oriented network to an emergency response oriented network. Successfully, with the use of the W-phase and other methods, the CSN has been able to report the Iquique and the Illapel earthquakes with an accurate magnitude just six minutes after the occurrence of both events. Now, the National Seismic Network is installed and methodologies that include the use of seismogeodetic data are being implemented.   The W-phase method and 3 methods of finite fault inversion are being implemented expecting that the RTX technology is accurate enough to be used for tsunami early warning purposes.

GNSS waveform tomography
Kristy Tiampo, University of Colorado, Boulder and  K. Kelevitz
  Today, seismic tomography is the primary tool used to learn about the interior structure and dynamics of the Earth (Thurber and Ritsema, 2015; Romanowicz, 2008; Boschi et al., 1996). However, the resolution of global seismic tomography models can suffer from insufficient coverage of the seismic network. However, GNSS data have been shown to be sensitive to earthquake ground motion and capable of recording surface wave waveforms (Larson, 2009; Houlié et al., 2011). In addition, GNSS receivers provide data at long periods, outside the range of most broadband seismometer records. Incorporation of the large number of permanently recording, high-rate (1 Hz) GNSS stations can improve the coverage and resolution of seismic tomography models.

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