Jennifer S. Haase

Modeling the rupture process of the 2003 September 25 Tokachi‐Oki (Hokkaido) earthquake using 1‐Hz GPS data

Received 10 September 2004; accepted 3 October 2004; published 3 November 2004. [1] High-rateGPShasthepotentialtorecoverbothdynamic and static displacements accurately. We analyze 1-Hz GPS data recorded during the 2003 Tokachi-Oki earthquake. The 1-Hz GPS displacement waveforms show good agreement with integrated accelerometer records except for low frequency noise that are inherently present in integrated seismic records. The GPS waveforms were inverted to model the spatio-temporal evolution of the fault slip during the rupture. The slip is found to propagate downdip in the subduction zone with largest moment release 50 km northwest of the hypocenter. The region of largest slip agrees in general with traditional seismic studies, indicating that 1-Hz GPS can be used for finite fault studies. The 1-Hz GPS slip model shows clearer contrast with afterslip distributions than those inferred from strong motion data, possibly because 1-Hz GPS is more sensitive to cumulative slip distribution. INDEX TERMS: 1294 Geodesy and Gravity: Instruments and techniques; 7209 Seismology: Earthquake dynamics and mechanics; 7212 Seismology: Earthquake ground motions and engineering. Citation: Miyazaki, S., K. M. Larson, K. Choi, K. Hikima, K. Koketsu, P. Bodin, J. Haase, G. Emore, and A. Yamagiwa (2004), Modeling the rupture process of the 2003 September 25 Tokachi-Oki (Hokkaido) earthquake using 1-Hz GPS data, Geophys. Res. Lett., 31, L21603, doi:10.1029/ 2004GL021457.

The Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) Experiment: Scientific Basis, New Analysis Tools, and Some First Results

The principal hypotheses of a new model of tropical cyclogenesis, known as the marsupial paradigm, were tested in the context of Atlantic tropical disturbances during the National Science Foundation (NSF)-sponsored Pre-Depression Investigation of Cloud Systems in the Tropics (PREDICT) experiment in 2010. PREDICT was part of a tri-agency collaboration, along with the National Aeronautics and Space Administrations Genesis and Rapid Intensification Processes (NASA GRIP) experiment and the National Oceanic and Atmospheric Administrations Intensity Forecasting Experiment (NOAA IFEX), intended to examine both developing and nondeveloping tropical disturbances. During PREDICT, a total of 26 missions were flown with the NSF/NCAR Gulfstream V (GV) aircraft sampling eight tropical disturbances. Among these were four cases (Fiona, ex-Gaston, Karl, and Matthew) for which three or more missions were conducted, many on consecutive days. Because of the scientific focus on the Lagrangian nature of the tropical cyclogen...

Recovering Seismic Displacements through Combined Use of 1-Hz GPS and Strong-Motion Accelerometers

Retrieving displacement from seismic acceleration records is often difficult because unknown small baseline offsets in the acceleration time series will contaminate the doubly integrated record with large quadratic errors. One-hertz Global Positioning System (gps) position estimates and collocated seismic data are available from the 2003 M w 8 Tokachi-Oki (Hokkaido) earthquake. After a process of correcting for possible misorientation of the seismic sensors, an inversion method is used to simultaneously solve for ground displacement with both data sets as input constraints. This inversion method takes into account the presence of unknown offsets in the acceleration record, and the relatively large uncertainties in the estimated 1-Hz gps positions. In this study, 117 channels of seismic data were analyzed. Only 5% of the time does the static displacement retrieved from traditional baseline correction processing without gps information agree with the absolute displacement measured with 1-Hz gps to within the errors of the gps data. In solving simultaneously for constrained displacements that agree with both the seismic and gps data sets, an optimal solution was found that included only one- or two-step functions in the acceleration records. Potential explanations for the offsets are analyzed in terms of tilt of the sensor or electronic noise. For nine stations, clear misorientations of the seismic sensors of more than 20 deg from the reported orientation were found. For this size event, the 30-sec sampled gps solutions were also a sufficient constraint for establishing the offset errors and recovering reliable displacements. The results significantly extend the frequency band over which accelerometer data are reliable for source inversion studies. Online material: Plots of constrained seismograms with metadata.

Accuracy and Variability of GPS Tropospheric Delay Measurements of Water Vapor in the Western Mediterranean

Abstract As a preliminary step for assessing the impact of global positioning system (GPS) refractive delay data in numerical weather prediction (NWP) models, the GPS zenith tropospheric delays (ZTDs) are analyzed from 51 permanent GPS sites in the western Mediterranean. The objectives are to estimate the error statistics necessary for future assimilation of GPS ZTD data in numerical models and to investigate the variability of the data in this area. The time series, which were derived continuously from November 1998 to June 2001, are compared with independent equivalent values derived from radiosonde profiles and the High-Resolution Limited-Area Model (HIRLAM) NWP model. Based on over two years of data, the difference between radiosonde and GPS ZTD has a standard deviation of 12 mm of delay and a bias of 7 mm of delay. Some sites have biases as high as 14 mm of delay. The bimodal distribution of residuals, with a higher bias for daytime launches, indicates these biases may be due to radiosonde day–night ...

The Concordiasi Project in Antarctica

The Concordiasi project is making innovative observations of the atmosphere above Antarctica. The most important goals of the Concordiasi are as follows: To enhance the accuracy of weather prediction and climate records in Antarctica through the assimilation of in situ and satellite data, with an emphasis on data provided by hyperspectral infrared sounders. The focus is on clouds, precipitation, and the mass budget of the ice sheets. The improvements in dynamical model analyses and forecasts will be used in chemical-transport models that describe the links between the polar vortex dynamics and ozone depletion, and to advance the under understanding of the Earth system by examining the interactions between Antarctica and lower latitudes. To improve our understanding of microphysical and dynamical processes controlling the polar ozone, by providing the first quasi-Lagrangian observations of stratospheric ozone and particles, in addition to an improved characterization of the 3D polar vortex dynamics. Techni...

Reducing satellite orbit error effects in near real-time GPS zenith tropospheric delay estimation for meteorology

We investigate the influence of using IGS predicted orbits for near real-time zenith tropospheric delay determination from GPS and implement a new processing strategy that allows the use of predicted orbits with minimal degradation of the ZTD estimates. Our strategy is based on the estimation of the three Keplerian parameters that represent the main error sources in predicted orbits (semi-major axis, inclination, and argument of perigee), and their associated variance directly from the real-time GPS data set. A comparison with the use of IGS final orbits shows a negligible bias and an rms less than 6 mm in the ZTD estimates at all the stations. The improvement compared to a strategy based only on the quality index provided with the predicted orbits is 20%. The level of accuracy and turn-around time shown here meet the current requirements for operational meteorology.

Seismogeodesy of the 2014 Mw6.1 napa earthquake, California: Rapid response and modeling of fast rupture on a dipping strike‐slip fault

Real-time high-rate geodetic data have been shown to be useful for rapid earthquake response systems during medium to large events. The 2014 Mw6.1 Napa, California earthquake is important because it provides an opportunity to study an event at the lower threshold of what can be detected with GPS. We show the results of GPS-only earthquake source products such as peak ground displacement magnitude scaling, centroid moment tensor (CMT) solution, and static slip inversion. We also highlight the retrospective real-time combination of GPS and strong motion data to produce seismogeodetic waveforms that have higher precision and longer period information than GPS-only or seismic-only measurements of ground motion. We show their utility for rapid kinematic slip inversion and conclude that it would have been possible, with current real-time infrastructure, to determine the basic features of the earthquake source. We supplement the analysis with strong motion data collected close to the source to obtain an improved postevent image of the source process. The model reveals unilateral fast propagation of slip to the north of the hypocenter with a delayed onset of shallow slip. The source model suggests that the multiple strands of observed surface rupture are controlled by the shallow soft sediments of Napa Valley and do not necessarily represent the intersection of the main faulting surface and the free surface. We conclude that the main dislocation plane is westward dipping and should intersect the surface to the east, either where the easternmost strand of surface rupture is observed or at the location where the West Napa fault has been mapped in the past.

Crustal Structure and Fault Geometry of the 2010 Haiti Earthquake from Temporary Seismometer Deployments

Haiti has been the locus of a number of large and damaging historical earthquakes. The recent 12 January 2010 Mw 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M 7 or larger earthquakes. Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, however, showed that the event ruptured a previously unmapped fault, the Leogâne fault, a north‐dipping oblique transpressional fault located immediately north of the EPGF. Following the earthquake, several groups installed temporary seismic stations to record aftershocks, including ocean‐bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, determine a 1D regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined dataset clearly delineate the Leogâne fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first‐motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.

Profiling the Atmosphere Using the Airborne GPS Radio Occultation Technique: A Sensitivity Study

Global Positioning System (GPS) radio occultation (RO) sounding, with its high vertical resolution temperature and humidity profiling capability, is revolutionizing atmospheric science, particularly through assimilation in numerical weather prediction (NWP) models. Currently, the observations are derived from GPS receivers onboard low Earth orbiting satellites. However, with the current number of satellites, it is difficult to provide dense sounding measurements in a specific region within a limited time period. With a GPS receiver onboard an airplane, the GPS RO technique offers such an opportunity while retaining the high vertical resolution sounding capability. The GNSS Instrument System for Multistatic and Occultation Sensing is currently under development for the National Science Foundations High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) aircraft. This paper presents a sensitivity analysis of the airborne occultation technique that will be used for the HIAPER system. The results demonstrate an anticipated overall accuracy of better than 0.5% for the retrieved refractivity from the surface to about 1 km below the airplane, where the expected airplane velocity errors of up to 5 mm/s limit the accuracy. The effects on the retrievals due to horizontal variations in atmospheric refractivity are significant, and retrieval errors may reach several percent inside frontal systems when the front is perpendicular to the ray paths and within 200 km of the tangent point. In general, the airborne GPS RO system provides a promising new data source for NWP and targeted observational studies.

The contributions of the MAGIC project to the COST 716 objectives of assessing the operational potential of ground-based GPS meteorology on an international scale

Abstract MAGIC (Meteorological Applications of GPS Integrated Column Water Vapor Measurements in the Western Mediterranean) is a 3 year project financed in part by the European Commission for research on deriving and validating robust GPS integrated water vapor (IWV) and zenith tropospheric delay (ZTD) data sets and developing methods to assimilate the data into numerical weather prediction models (NWP) and test their impact. It was conceived independently from the COST 716 action, which seeks to coordinate research in the domain at an international scale, but addresses some of the same objectives. This has led to a productive cooperation between the two initiatives and their participants, and motivated the decision of MAGIC participants to provide research results as part of the COST demonstration system. Currently a database of 1.5 years of ZTD data are available on the MAGIC web site which has been validated through comparisons with radiosondes which gives differences with a standard deviation of 10 mm ZTD or the equivalent error in IWV of 1.6 kg/m2. NWP assimilation tests will be carried out in the final year of the project.