Publications

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2018
Saunders, JK, Haase JS.  2018.  Augmenting onshore GNSS displacements with offshore observations to improve slip characterization for Cascadia Subduction Zone earthquakes. Geophysical Research Letters. 45:6008-6017.   10.1029/2018gl078233   AbstractWebsite

For the Cascadia subduction zone, M-w similar to 8 megathrust earthquake hazard is of particular interest because uncertainties in the predicted tsunami size affect evacuation alerts. To reduce these uncertainties, we examine how augmenting the current Global Navigation Satellite Systems (GNSS) network in Cascadia with offshore stations improves static slip inversions for M-w similar to 8 megathrust earthquakes at different rupture depths. We test two offshore coseismic data types: vertical-only bottom pressure sensors and pressure sensors combined with GNSS-Acoustic aided horizontal positions. We find that amphibious networks best constrain slip for a shallow earthquake compared to onshore-only networks when offshore stations are located above the rupture. However, inversions using vertical-only offshore data underestimate shallow slip and tsunami impact. Including offshore horizontal observations improves slip estimates, particularly maximum slip. This suggests that while real-time GNSS-Acoustic sensors may have a long development timeline, they will have more impact for static inversion-based tsunami early warning systems than bottom pressure sensors. Plain Language Summary The Cascadia subduction zone is the region of highest tsunami hazard within the contiguous United States. This region has experienced many tsunamis over the last 10,000years that were generated by earthquakes of magnitude 8 to 9. Magnitude 8 earthquakes in the subduction zone can be tricky for tsunami early warning systems because it is difficult to determine the depth of the earthquake rupture, which strongly affects the anticipated tsunami size. This can make the difference between an evacuation order being issued or not. This study tests how estimating total slip on the earthquake fault during rupture and the resulting tsunami wave height for magnitude 8 earthquakes can be improved when combining the current land-based Global Navigation Satellite Systems monitoring network in the Pacific Northwest with offshore seafloor networks. We test hypothetical arrangements of offshore stations that measure the vertical seafloor motion with ocean bottom pressure sensors. We also test networks that measure motion in all three directions by including Global Navigation Satellite Systems measurements at the sea surface linked by acoustic communication to measurement points on the seafloor. This work can help plan where best to put new offshore instruments as they are developed for future tsunami early warning systems.

2016
Zhang, WX, Haase JS, Hertzog A, Lou YD, Vincent R.  2016.  Improvement of stratospheric balloon GPS positioning and the impact on gravity wave parameter estimation for the Concordiasi campaign in Antarctica. Journal of Geophysical Research-Atmospheres. 121:9977-9997.   10.1002/2015jd024596   AbstractWebsite

Gravity waves (GWs) play an important role in transferring energy and momentum from the troposphere to the middle atmosphere. However, shorter-scale GWs are generally not explicitly resolved in general circulation models but need to be parameterized instead. Super pressure balloons provide direct access to measure GW characteristics as a function of wave intrinsic frequency that are needed for these parameterizations. The 30s sampling rate of the GPS receivers carried on the balloons deployed in the 2010 Concordiasi campaign in the Antarctic is much higher compared to the previous campaigns and can cover the full range of the GW spectrum. Two among 19 balloons are also equipped with the dual-frequency GPS receivers initially developed for GPS radio occultation research in addition to the single-frequency receivers, which are expected to provide better positions for GW parameter estimations. Improvements of the positions are significant, from similar to 3-10m horizontal and similar to 5m vertical to similar to 0.1 and 0.2m, respectively, which makes it possible to resolve the Eulerian pressure independently of altitude for the intrinsic phase speed estimation. The lower position accuracy in the previous analysis of campaign results from the single-frequency GPS receiver was primarily due to a problem with the onboard clock that is not present in the new results. The impacts of the position improvements on the final GW parameters are highlighted, with larger difference in momentum flux for the shorter-scale GWs than for the longer scale GWs and significant difference in the distribution of the intrinsic phase speed.

2013
Symithe, SJ, Calais E, Haase JS, Freed AM, Douilly R.  2013.  Coseismic slip distribution of the 2010 m 7.0 Haiti earthquake and resulting stress changes on regional faults. Bulletin of the Seismological Society of America. 103:2326-2343.   10.1785/0120120306   AbstractWebsite

The 12 January 2010 M-w 7.0 Haiti earthquake ruptured the previously unmapped Leogane fault, a secondary transpressional structure located close to the Enriquillo fault, the major fault system assumed to be the primary source of seismic hazard for southern Haiti. In the absence of a precise aftershock catalog, previous estimations of coseismic slip had to infer the rupture geometry from geodetic and/or seismological data. Here we use a catalog of precisely relocated aftershocks beginning one month after the event and covering the following 5 months to constrain the rupture geometry, estimate a slip distribution from an inversion of Global Positional Systems (GPS), Interferometric Synthetic Aperture Radar (InSAR) and coastal uplift data, and calculate the resulting changes of Coulomb failure stress on neighboring faults. The relocated aftershocks confirm a north-dipping structure consistent with the Leogane fault, as inferred from previous slip inversions, but with two subfaults, each corresponding to a major slip patch. The rupture increased Coulomb stresses on the shallow Enriquillo fault parallel to the Leogane rupture surface and to the west (Miragoane area) and east (Port-au-Prince). Results show that the cluster of reverse faulting earthquakes observed further to the west, coincident with the offshore Trois Baies fault, are triggered by an increase in Coulomb stress. Other major regional faults did not experience a significant change in stress. The increase of stress on faults such as the Enriquillo are a concern, as this could advance the timing of future events on this fault, still capable of magnitude 7 or greater earthquakes.

Crowell, BW, Melgar D, Bock Y, Haase JS, Geng JH.  2013.  Earthquake magnitude scaling using seismogeodetic data. Geophysical Research Letters. 40:6089-6094.   10.1002/2013gl058391   AbstractWebsite

The combination of GPS and strong-motion data to estimate seismogeodetic waveforms creates a data set that is sensitive to the entire spectrum of ground displacement and the full extent of coseismic slip. In this study we derive earthquake magnitude scaling relationships using seismogeodetic observations of either P wave amplitude or peak ground displacements from five earthquakes in Japan and California ranging in magnitude from 5.3 to 9.0. The addition of the low-frequency component allows rapid distinction of earthquake size for large magnitude events with high precision, unlike accelerometer data that saturate for earthquakes greater than M 7 to 8, and is available well before the coseismic displacements are emplaced. These results, though based on a limited seismogeodetic data set, support earlier studies that propose it may be possible to estimate the final magnitude of an earthquake well before the rupture is complete.

2008
Chen, SH, Zhao Z, Haase JS, Chen AD, Vandenberghe F.  2008.  A study of the characteristics and assimilation of retrieved MODIS total precipitable water data in severe weather simulations. Monthly Weather Review. 136:3608-3628.   10.1175/2008mwr2384.1   AbstractWebsite

This study determined the accuracy and biases associated with retrieved Moderate Resolution Imaging Spectroradiometer (MODIS) total precipitable water (TPW) data, and it investigated the impact of these data on severe weather simulations using the Weather Research and Forecast (WRF) model. Comparisons of MODIS TPW with the global positioning system (GPS) TPW and radiosonde-derived TPW were carried out. The comparison with GPS TPW over the United States showed that the root-mean-square (RMS) differences between these two datasets were about 5.2 and 3.3 mm for infrared (IR) and near-infrared (nIR) TPW, respectively. MODIS IR TPW data were overestimated in a dry atmosphere but underestimated in a moist atmosphere, whereas the nIR values were slightly underestimated in a dry atmosphere but overestimated in a moist atmosphere. Two cases, a severe thunderstorm system (2004) over land and Hurricane Isidore (2002) over ocean, as well as conventional observations and Special Sensor Microwave Imager (SSM/I) retrievals were used to assess the impact of MODIS nIR TPW data on severe weather simulations. The assimilation of MODIS data has a slightly positive impact on the simulated rainfall over Oklahoma for the thunderstorm case, and it was able to enhance Isidore's intensity when the storm track was reasonably simulated. The use of original and bias-corrected MODIS nIR TPW did not show significant differences from both case studies. In addition, SSM/I data were found to have a positive impact on both severe weather simulations, and the impact was comparable to or slightly better than that of MODIS data.

2002
Healy, SB, Haase J, Lesne O.  2002.  Abel transform inversion of radio occultation measurements made with a receiver inside the Earth's atmosphere. Annales Geophysicae. 20:1253-1256. AbstractWebsite

Radio occultation measurements made with a receiver inside the Earth's atmosphere can be inverted, assuming local spherical symmetry, with an Abel transform to provide an estimate of the atmospheric refractive index profile. The measurement geometry is closely related to problems encountered when inverting seismic time-travel data and solar occultation measurements, where the Abel solution is well known. The method requires measuring both rays that originate from above and below the local horizon of the receiver. The Abel transform operates on a profile of "partial bending angles" found by subtracting the positive elevation measurement from the negative elevation value with the same impact parameter. In principle, the refractive index profile can be derived from measurements with a single frequency GPS receiver because the ionospheric bending is removed when the partial bending angle is evaluated.

Ge, MR, Calais E, Haase J.  2002.  Sensitivity of zenith total delay accuracy to GPS orbit errors and implications for near-real-time GPS meteorology. Journal of Geophysical Research-Atmospheres. 107   431510.1029/2001jd001095   AbstractWebsite

[1] Global Positioning System (GPS) measurements have been demonstrated to provide precipitable water vapor (PWV) estimates with a level of accuracy that is comparable to that of radiosondes and microwave radiometers. GPS measurements therefore have the potential to become a significant source of data for operational weather forecasting, provided that PWV (or the intermediate zenith total delay (ZTD)) can be made available in near real-time with a minimum accuracy degradation. Despite the recent decrease in the latency and increase in accuracy provided by the International GPS Service (IGS) ultrarapid predicted GPS orbit products, we show that the accuracy of these orbits continues to be a limiting factor for the accuracy of near real-time GPS-derived atmospheric estimates. In this work, a coefficient matrix is derived from the normal equations of the least squares adjustment model for the GPS observables that maps the orbital parameter errors into ZTD errors. This is used to analyze the sensitivity of GPS derived tropospheric errors to an extensive set of parameters, including their time dependence, in a computationally efficient manner. We show that ZTD errors are dominated by biases in the orbital semimajor axis, with minor contributions from the inclination and argument of perigee, and that this error increases significantly after the fourth to fifth hour of the prediction window. We implemented a GPS data processing strategy based on an iterative estimation of the three most critical orbital parameters (semimajor axis, inclination and argument of perigee) together with the ZTD parameters. We tested this strategy in a 3500 3500 km network of 15 GPS sites in western Europe providing hourly data files. We show that the standard deviation improvement compared to a strategy based only on the orbit quality index provided with the predicted orbit products is on the order of 20%. The analysis of one month of data in near-real-time shows a bias lower than 1 mm ZTD and a standard deviation lower than 6 mm ZTD compared to using the most precise IGS final orbits. We also show that this strategy is robust and capable of dealing with very large orbit errors appropriately. We demonstrate that the same quality is achievable with a 1500 1500 km network which has positive implications for decentralized processing strategies. The near real-time processing methodology described here meets the current timeliness requirements of operational meteorology (30 mn to 2 hours, depending on the application), while ensuring a level of accuracy similar to that provided in postprocessed mode with precise final IGS orbits (1 mm ZTD bias, 6 mm ZTD RMS). The method we propose can also be considered as an "on-the-fly'' orbit quality control for near real-time GPS applications.