Dr. Yuning Fu

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Dr. Yuning Fu

Assistant Professor in Geophysics

Department of Geology

School of Earth, Environment and Society

Bowling Green State University

Email: yfu(at)bgsu(dot)edu

I am ...

Assistant Professor in Geophysics, Bowling Green State University.

I am studying tectonic and nontectonic crustal deformation using geodetic measurements.

... (email me if you want to know more, or opportunity for graduate student working with me)

Current Research

Estimate water storage variations in the western U.S. with geodetic measurements.

Long-term and short-term Slow Slip Events (SSE) in the southern central Alaska subduction zone.

Seasonal and long-term vertical deformation in Asia and southern Alaska constrained by GPS and GRACE measurements.

Ocean Tidal Loading and its effect on GPS coordiante solutions.

Hydrological mass transportation (seasonal plus long-term) and its loading effect in Asia and Alaska.

Tsunamis and gravity changes caused by large earthquakes.

Highlight

Graduate student Andrew Watkins's paper published in Nature Scientific Reports. Earth's Subdecadal Angular Momentum Balance from Deformation and Rotation Data. Congratulations, Andrew!

Paper published in Pure Appl. Geophys. on Linking Oceanic Tsunamis and Geodetic Gravity Changes of Large Earthquakes.

Paper published in Science on Seasonal water storage, stress modulation, and California seismicity.

Paper published in G-Cubed on spatio-temporal variations of the Slow Slip Event between 2008 and 2013.

Paper published in JGR on terrestrial water storage change estimated from GPS measurements of loading deformation.

Paper in GRL on seasonal horizontal motion in the Amazon Basin and in Southeast Asia Observed by GPS and Inferred from GRACE.

Received the NASA Postdoctoral Program Fellowship.

Finished Ph.D degree at the University of Alaska Fairbanks.

AGU Outstanding Student Paper Awards. Geodesy Section. 2011 Fall Meeting. [See webpage].

The Global Change Student Grant Award. [See webpage]

2011-2012 Best Student Publication Award, Geophysical Institute, University of Alaska Fairbanks. [See photo]

Best Student Poster in Geophysics, Alaska Geology Society (AGS) 2012 Technical Conference [See webpage].

2nd place of best poster presentation in the Midnight Sun Science Symposium. [See webpage]

We identify and study an ongoing Slow Slip Event (SSE) in the southcentral Alaska subduction zone using GPS measurements. This is the second large SSE in this region since modern geodetic measurements became available in 1993. We divide the ongoing SSE into two phases according to their transient displacement time evolution; their slip distributions are similar to each other but slip rates are slightly different. This ongoing SSE occurs downdip of the main asperity that ruptured in the 1964 Alaska earthquake, on the same part of the subduction interface as the earlier 1998–2001 SSE. The average slip rate of this SSE is ～4–5cm/yr, with a cumulative moment magnitude of Mw 7.5 (Mw 7.3 and Mw 7.1 For Phases I and II, respectively) through the end of 2012. The time and space dependence of the GPS displacements suggest that the slip area remained nearly the same during Phase I, while the slip rate increased with time. The SSEs occur on a transitional section of the subduction plate interface between the fully locked updip part and the freely slipping deeper part. During the 1964 earthquake, slip on the region of the SSE was much lower than slip in the updip region. Based on this observation and the repeated SSEs, we conclude that this part of the interface slips repeatedly in SSEs throughout the interseismic period and does not build up a large slip deficit to be released through large slip in earthquakes.

Please see our paper in EPSL [pdf].

Slip distribution for the whole event through the end of 2012. The black star indicates the location of Anchorage. The dashed lines show the locations of the previous 1998–2001 SSE in black, and the 2010–2011 event in magenta. The blue dashed line highlights the rupture area of the Alaska 1964 earthquake.

We compare vertical seasonal loading deformation observed by continuous GPS stations in southern Alaska and modeled vertical displacements due to seasonal hydrological loading inferred from GRACE. Seasonal displacements are significant, and GPS-observed and GRACE-modeled seasonal displacements are highly correlated. We define a measure called the WRMS Reduction Ratio to measure the fraction of the position variations at seasonal periods removed by correcting the GPS time series using a seasonal model based on GRACE. The median WRMS Reduction Ratio is 0.82 and the mean is 0.73 ± 0.26, with a value of 1.0 indicating perfect agreement of GPS and GRACE. The effects of atmosphere and non-tidal ocean loading are important; we add the AOD1B de-aliasing model to the GRACE solutions because the displacements due to these loads are present in the GPS data, and this improves the correlations between these two geodetic measurements. We find weak correlations for some stations located in areas where the magnitude of the load changes over a short distance, due to GRACE’s limited spatial resolution. GRACE models can correct seasonal displacements for campaign GPS measurements as well.

Please see our paper in Geophysical Research Letter [pdf].

Distribution of continuous GPS stations (blue diamonds) in southern Alaska; Three examples (AC06, ELDC and LEVC) of GPS vertical seasonal (detrended) timeseries and their GRACE-modeled seasonal vertical displacements are shown.

The WRMS Reduction Ratios for all continuous GPS stations in southern Alaska. The Ellipse (northwest) highlights low-elevation coastal stations of Cook Inlet, where GRACE consistently overestimates the amplitude of the seasonal variations.

We analyze continuous GPS measurements in Nepal, southern side of the Himalaya, and compare GPS results with GRACE observations in this area. We find both GPS and GRACE show significant seasonal variations. Further comparison indicates that the observed seasonal GPS height variation and GRACE-derived seasonal vertical displacement due to the changing hydrologic load exhibit very consistent results, for both amplitude and phase. For continuous GPS stations whose observation time span are longer than 3 years, the average WRMS reduction is ~45% when we subtract GRACE-derived vertical displacements from GPS observed timeseries. The comparison for annual amplitudes between GPS observed and GRACE-derived seasonal displacements also shows consistent correlation. The good seasonal correlation between GPS and GRACE is due to the improved GPS processing strategies and also because of the strong seasonal hydrological variations in Nepal. Besides the seasonal signal, GRACE also indicates a long-term mass loss in the Himalaya region, assuming no GIA effect. This mass loss therefore will lead to crustal uplift since the earth behaves as an elastic body. We model this effect and remove it from GPS observed vertical rates. With a 2D dislocation model, most GPS vertical rates, especially in the central part of Nepal, can be interpreted by interseismic strain from the Main Himalayan Thrust, and several exceptions may indicate the complexity of vertical motion in this region and some potential local effects.

Please See our paper in Journal of Geophysical Research [pdf], or contact the authors Yuning Fu and Jeff Freymueller.

Stacked 10-day averaged GPS seasonal (detrended) vertical timeseries and GRACE-derived seasonal vertical timeseries.

Stacked GPS seasonal (detrended) horizontal timeseries and GRACE-derived seasonal horizontal timeseries.

Vertical velocities after subtracting the GRACE-derived long-term uplift rate due to load changes.

We use up to a 6-year span of GPS data from 85 globally distributed stations to compare solutions using ocean tidal loading (OTL) corrections computed in different reference frames: center of mass of the solid Earth (CE), and center of mass of the Earth system (CM). We compare solution sets that differ only in the frame used for the OTL model computations, for three types of GPS solutions. In global solutions with all parameters including orbits estimated simultaneously, we find coordinate differences of ~0.3 mm between solutions using OTL computed in CM and OTL computed in CE. When orbits or orbits and clocks are fixed, larger biases appear if the user applies an OTL model inconsistent with that used to derive the orbit and clock products. Network solutions (orbits fixed, satellite clocks estimated) show differences smaller than 0.5 mm due to model inconsistency, but PPP solutions show distortions at the ~1.3 mm level. The much larger effect on PPP solutions indicates that satellite clock estimates are sensitive to the OTL model applied. The time series of coordinate differences shows a strong spectral peak at a period of ~14 days when inconsistent OTL models are applied and smaller peaks at ~annual and ~semi-annual periods, for both ambiguity-free and ambiguity-fixed solutions. These spurious coordinate variations disappear in solutions using consistent OTL models. Users of orbit and clock products must ensure that they use OTL coefficients computed in the same reference frame as the OTL coefficients used by the analysis centers that produced the products they use; otherwise, systematic errors will be introduced into position solutions. All modern products should use loading models computed in the CM frame, but legacy products may require loading models computed in the CE frame. Analysts and authors need to document the frame used for all loading computations in product descriptions and papers.

Want to know more, please read our paper published in Journal of Geodesy [pdf], or contact the authors Yuning Fu, Jeff Freymueller and Tonie van Dam.

Differences between GPS solutions determined using OTL-CM and OTL-CE coefficients, for the station TIDB.

Stacked power spectrum showing the ~14-day period component of 1-year detrended vertical coordinate timeseries.