Leader: Jessica Murray
Co-Leader: David Sandwell

Research Objectives

Tectonic Geodesy activities in SCEC4 will focus on data collection and analysis that contribute to improved earthquake response and to a better understanding of fault loading and stress transfer, the causes and effects of transient deformation, and the structure and evolution of fault zones and systems.

Research Strategies

• Contribute to the development of a Community Geodetic Model (CGM). The goal of this effort is to develop a geodetic time series data product for southern California that leverages the complementary nature of GPS and InSAR observations. This will require development of optimal methods for combining GPS and InSAR data, characterizing seasonal/hydrologic/anthropogenic signals, incorporating new data, and accounting for earthquake effects as needed. Proposals should demonstrate coordination with the current activities and established timeline of the CGM project. Proposals that target participation in ongoing GPS and InSAR time series analysis comparison exercises, compilation of a comprehensive set of campaign and continuous GPS time series for southern California, or identification of optimal approaches for mitigating temporally and spatially correlated noise in GPS or InSAR time series are particularly encouraged. More information can be found here.
• Analysis of geodetic data to address specific SCEC4 research targets. Studies addressing geodetic/geologic slip rate discrepancies, assessing the role of lower crust/upper mantle processes in driving fault loading, developing more physically realistic deformation models, providing input to the development of Community Stress Models, and constraining physics-based models of slow slip and tremor are encouraged, as are studies that pursue integrated use of geodetic, geologic, seismic, and other observations targeting special fault study areas. Proposals that include collection of new data should explicitly motivate the need for such efforts. In compliance with SCEC's data policy, data collected with SCEC funding must be made publicly available upon collection by archiving at an appropriate data center, preferably UNAVCO (contact Jessica Murray for further information on archiving). Annual reports should include a description of archive activities.
• Improve our understanding of the processes underlying detected transient deformation signals and/or their seismic hazard implications through data collection and development of new analysis tools. Work that advances methods for near-real-time transient detection and applies these algorithms within the SCEC transient detection testing framework to search for transient deformation in southern California is encouraged. Approaches that can be automated or semi-automated are the highest priority, as is their inclusion in the testing framework now in place at SCEC (contact Rowena Lohman for details on how to address this in the proposal). Extension of methods to include InSAR and strainmeter data and, when available, the CGM is also a priority. Work that develops means for incorporating the output of transient detection algorithms into time-dependent earthquake forecasting is encouraged.
• Develop and apply algorithms that use real-time high-rate GPS data in concert with seismic data for improved earthquake response. We encourage proposals that explore new approaches for assimilating real-time high-rate GPS, seismic data, and other potential observations into efforts to rapidly characterize earthquake sources. Also of interest is the development and application of rigorous retrospective and prospective tests to evaluate algorithm performance.

Recent Results

Figure 1. Densification of GPS data. GPS marks that have been occupied multiple times and may therefore provide spatial dense geodetic velocities. A primary goal of future CGM work is to identify such sites and archive or process the available data [Herring and Floyd, personal communication, 2014].

Figure 2. InSAR time series. Mosaic view of the mean LOS velocity map of descending tracks 170, 399, 127, 356, and 84 from combining ERS-1/2 and Envisat data. Note that certain tracks are displayed with ERS LOS map only to not show coseismic deformation signals of the Hector Mine earthquake. Differential LOS time series between b(t) and B(t) across East California Shear Zone show long term transient that is likely related to postseismic relaxation of Lander and Hector Mine earthquakes.

Figure 3. Refined near-fault creep measurements. Envisat InSAR and survey-mode GPS observations reveal the pattern of uplift and shallow fault creep along the southernmost San Andreas Fault. (a) Vertical ground velocity from Envisat, using a combination of ascending (Track 77) and descending (Track 356) InSAR observations. BC denotes the Bat Caves Buttes leveling line, which recorded a similar rate of uplift [Sylvester et al., 1993]. Note also areas of subsidence related to hydrologic processes. (b) Fault-parallel ground velocity from Envisat. Diamonds indicate creepmeters at North shore, Ferrum (Fe), Salt Creek (SC), and Durmid Hill (DH), operated by Univ. Colorado at Boulder. Triangles show locations of GPS monuments at Painted Canyon. (c) Comparison of InSAR velocities with GPS at Painted Canyon. The InSAR data are in good agreement with ground-based observations, and reveal that creep occurs along the entire fault segment. Creep is localized on the fault trace only at Durmid Hill and Mecca Hills, where the local fault strike leads to transpression and a high fault-normal stress. At Bombay Beach and North Shore, decreased normal stress may lead to distributed yielding — in these areas creep is distributed across a 1-2 km wide zone. (Lindsey et al., J. Geophys. Res., in review).

Figure 4. Collaborative surveys of El Major Cucapah postseismic deformation. Within one day of the rupture scientists from CICESE, UCSD and UCR began campaign surveys in the near field of the EMC rupture zone and have continued these measurements for more than 3 years to capture these postseismic transients. [Gonzales-Ortega et al., 2014] Daily GPS positions for the four sites closest to the earthquake rupture. The north and east components of the displacement vector are denoted by the green and blue symbols, respectively. The best fitting exponential, logarithmic, and hyperbolic cotangent functions are indicated by the black dashed, black dotted, and solid red lines, respectively. Also shown are the corresponding relaxation times (τ).

Tectonic Geodesy activities in SCEC4 are focusing on data collection and analysis that contribute to improved earthquake response and to a better understanding of fault loading and stress transfer, the causes and effects of transient deformation, and the structure and evolution of fault zones and systems. Work by the SCEC community in the area of Tectonic Geodesy this year has focused on three areas: development of a Community Geodetic Model (CGM), earthquake early warning, and automated transient detection algorithms, and the analysis of high resolution geodetic data.

Community Geodetic Model

Densification of GPS arrays as part of Earthscope, the rapidly growing volumes of InSAR data from various satellites, and the development of time series analysis for InSAR data all motivated the development of a Community Geodetic Model (CGM), and we report here on progress in meeting science milestone 4. The CGM should improve geodetic studies of non-secular strain phenomena observed in Southern California, including post-seismic deformation. It will be distinct from the past SCEC Crustal Motion Map (CMM) because it will be time dependent and will incorporate InSAR data to constrain both the vertical deformation field and small-scale details of the regional deformation. This will lead to refined and improved tectonic geodesy data products for use in modeling. The CGM would be used in combination with other SCEC community models to infer the evolution of sub-surface processes. It will also provide a time-dependent reference frame for transient detection algorithms, as well as models of interseismic loading to evaluate stress changes and update rupture forecast models as tectonic conditions evolve in California.

The challenge of the CGM is to exploit the spatially sparse, temporally dense 3D GPS time series and spatially dense, temporally sparse InSAR line-of-site time series consistent with GPS time series in an appropriate projection. We note that the recent launch of two new InSAR satellites will greatly facilitate the development of InSAR time series by providing more accurate and frequent observations from multiple look directions at both C-band and L-band.

SCEC funded research in support of this effort is taking many forms including data collection to fill gaps in coverage, assessment of modeling approaches appropriate for our needs, and exploration of ways to mitigate noise and merge datasets.

California State University San Bernardino and University of Arizona researchers have teamed up to continue a field program started in 2002 that involves undergraduates and local teachers in collecting and interpreting GPS data in the San Bernardino mountains and surrounding area where previous data coverage was sparse. In addition, researchers at UC Riverside and MIT are using a dataset that combines campaign GPS data from their own field surveys with data from continuous networks and archives, to investigate the degree to which the San Jacinto Fault (SJF) slip rate varies along-strike. Continued efforts by MIT scientists to merge PBO and USGS continuous GPS solutions for southern California will prove vital in development of the CGM (Figure 1).

InSAR observations complement GPS by providing spatially dense deformation measurements. Ongoing work by this group aims to improve InSAR processing methods in order to mitigate decorrelation in areas that have experienced large coseismic offsets. Current research at Cornell is focused on integrating InSAR and GPS data into time varying deformation maps by mitigating the effects of atmospheric noise as well as using synthetic tests to explore the optimal ways to combine InSAR and GPS data. Scientists at NASA’s Jet Propulsion Laboratory are currently applying InSAR time series analysis techniques to 18 years of SAR data from southern California to produce a line-of-sight velocity map constrained by GPS in order to investigate time-varying deformation (Figure 2). Modeling of dense GPS and InSAR velocity transects crossing the Southern San Andreas Fault (SAF) by investigators at SIO and San Diego State University has revealed evidence for along-strike variations in the width and depth of the creeping segment (Figure 3).

The 2010 El Mayor Cucapah earthquake has provided opportunities to investigate crust and upper mantle rheology using geodetic observations of postseismic deformation. Data collection conducted through a collaboration between Scripps Institution of Oceanography (SIO), UC Riverside, and CISESE has resulted in an improved understanding of the afterslip following the El Mayor Cucupah earthquake (Figure 4).

Scientists at Appalachian State University, UC Riverside, JPL, and Harvard have coordinated efforts to better constrain fault slip rates and patterns of interseismic deformation in the western Transverse Ranges of southern California with a particular focus on the Ventura Special Fault Study Area. This has involved the combined analysis of GPS and InSAR data into a mechanical dislocation model to better constrain fault slip rates.

Ongoing collaborative activities of the CGM include:

1. First SCEC Community Geodetic Model (CGM) workshop (Menlo Park, CA, 30-31 May, 2013): This workshop (presentations available at: http://ceo.scec.org/workshops/2013/cgm) addressed the major problems and paths forwards towards generation of a joint GPS-InSAR 3-dimensional deformation field product. The workshop was summarized in a Meeting report in EOS, Volume 94, Number 35, 2013.
2. Focus Groups: We formed GPS and InSAR focus groups that will assess and validate potential time series generation approaches for the individual data types.
3. InSAR exercise: We initiated an exercise within the InSAR community to process data for a particular frame in Southern California, for the purposes of comparison of the result of different approaches, validation against GPS data and data from overlapping tracks, and assessment of the appropriate errors to use in joint GPS-InSAR efforts.
4. Second SCEC Community Geodetic Model (CGM) workshop – A second GPS/InSAR workshop will be held prior to the 2014 SCEC Annual Meeting and will include 20 participants. The workshop report will be available in October 2014.

Transient Detection and Early Warning

Scientists at UCSD have made progress in estimating the magnitude of an emergent earthquake by combining seismometers and GPS sensors to measure the full spectrum of the near-field strong motions. GPS-seismometer units will be deployed at several CRTN stations in southern California during the project period.

Scientists at MIT are refining a transient detection algorithm and have submitted our algorithms to the Colaboratory for the Study of Earthquake Predictability (CSEP) and they are now running operationally. A transient detection algorithm based time-dependent displacement gradient fields and statistical analysis of measured strain anomalies has been developed at Stony Brook University and is now implemented in the CSEP testing system. Scientists at Woods Hole Oceanographic institution are studying the 22 year history of aseismic creep transients on the Superstition Hills Fault. They found that models which included significant heterogeneity in the shallow frictional properties of the fault, can be consistent with both the afterslip and interseismic creep events observed on the Superstition Hills Fault.

Scientists at Stanford University are continuing to refine their transient detection algorithm through an improved understanding of the network noise processes. They have selected a set of 20 GPS stations over stable North America where the glacial isostatic signal provides a known, large scale secular signal. A better characterization of the noise in this stable environment will help to refine the network-based transient detection algorithms being deployed in Southern California.

High-resolution Geodetic Measurements

PBO borehole strainmeters in the Anza region and the laser strainmeters at the Pinon Flat Observatory continue to provide high-resolution observations of transient behavior associated with southern California earthquakes. Triggered aseismic slip on the San Jacinto fault has been inferred from these data to have occurred following the 2005 Anza earthquake and again after the El Mayor Cucapah earthquake at the southern end of the Anza gap. Transient deformation consistent with aseismic slip during 2010 – 2011 at the location of the 2005 earthquake has also been observed. A March 2013 M4.7 event on the San Jacinto fault near Anza triggered strain rate changes indicative of fault parallel shear with short duration (1 – 2 hour) slip accelerations. Further analysis and modeling will be required to investigate causes of observed variability in the occurrence and timing of strain recorded at different locations following the same events.

Select Publications

• Arrowsmith, R., C. Crosby, E. Kleber, E. Nissen, and P. Gold, (2013), Imaging and Analyzing Southern California’s Active Faults with Lidar, November 4-6, 2013 San Diego Supercomputer Center (SDSC), UCSD, La Jolla, CA.
• Arrowsmith, R., K. Okumura, E. Nissen, T. Maruyama, C. Crosby, M. Oskin, S. Toda (2013), VISES SCEC Workshop on High Resolution Topography Applied to Earthquake Studies, September 18-20, 2013 Earthquake Research Institute (ERI), The University of Tokyo, Japan; September 21, 2013, Center for Spatial Information Science, The University of Tokyo, Japan.
• Agnew, D. C. (2014). Variable Star Symbols for Seismicity Plots, Seismol. Res. Lett., v. 85, p. 775-780. SCEC Contribution 1931
• Agnew, D. C. and F. K. Wyatt (2014). Dynamic Strains at Regional and Teleseismic Distances, Bull. Seismol. Soc. Amer., in revision. SCEC Contribution 1938
• Crowell, B. W., Y. Bock, D. T. Sandwell, and Y. Fialko (2013), Geodetic investigation into the deformation of the Salton Trough, J. Geophys. Res. Solid Earth, 118, 5030–5039, doi:10.1002/jgrb.50347. SCEC Contribution 1749
• Dmitrieva, K., and P. Segall (2014), Network-based estimator of time-dependent GPS noise, in preparation.
• Gonzalez-Ortega, A., Y. Fialko, D. Sandwell, F. A. Nava-Pichardo, J. Fletcher, J. Gonzalez-Garcia, B. Lipovsky, M. Floyd, G. Funning (2014), El Mayor-Cucapah (Mw 7.2) earthquake: Early near-field postseismic deformation from InSAR and GPS observations, J. Geophys. Res., doi:10.1002/2013JB010193. SCEC Contribution 2014
• Ji, K. H. and T. A. Herring, Testing Kalman Smoothing/PCA Transient Signal Detection Using Synthetic Data, Seismol. Res. Letters, May/June 2013, 84, 433-443, doi:10.1785/0220120155, 2013. SCEC Contribution 1834
• Johnson, K., Nissen, E., Saripalli, S., Arrowsmith, J R., McGarey, P., Scharer, K., Williams, P., and Blisniuk, K., in review. Rapid mapping of ultra-fine fault zone topography with Structure from Motion, submitted to Geosphere, December 2013. SCEC Contribution 1921
• Lindsey, E., V. Sahakian, Y. Fialko, Y. Bock, S. Barbot, and T. Rockwell (2013), Interseismic Strain Localization in the San Jacinto Fault Zone, Pure and Appl. Geophys., doi:10.1007/s00024-013- 0753-z. SCEC Contribution 1929
• Liu, Z., P. Lundgren, Z. K. Shen, 2014, Improved imaging of Southern California crustal deformation using InSAR and GPS, SCEC Annual Meeting, Palm Springs, California SCEC Contribution 2038
• McGill, S. F., Spinler, J.C., McGill, J.D., Bennett, R.A., Floyd, M., Fryxell, J. and Funning, G., (in prep.), One-dimensional modeling of fault slip rates using new geodetic velocities from a transect across the plate boundary through the San Bernardino Mountains, in preparation for submission to Journal of Geophysical Research in Spring 2014. SCEC Contribution 1995
• Marshall, S. T., G. J. Funning, and S. E. Owen (2013), Fault slip rates and interseismic deformation in the western Transverse Ranges, CA, Journal of Geophysical Research, 118, 4511-4534. doi: 10.1002/jgrb.50312. SCEC Contribution 1744
• Melgar, D. and Y. Bock (2013), Near-Field Tsunami Models with Rapid Earthquake Source Inversions from Land and Ocean Based Observations: The Potential for Forecast and Warning, J. Geophys. Res., 118, doi:10.1102/2013JB010506. SCEC Contribution 1996
• Melgar, D., B. W. Crowell, Y. Bock, and J. S. Haase (2013), Rapid modeling of the 2011 Mw 9.0 Tohoku-oki earthquake with seismogeodesy, Geophys. Res. Lett., 40, 1-6, doi:10.1002/grl.50590. SCEC Contribution 1934
• Melgar, D., Y. Bock, D. Sanchez and B. W. Crowell (2013b), On robust and reliable automated baseline corrections for strong motion seismology, J. Geophys. Res., 118, doi:10.1029/2012JB009937. SCEC Contribution 1731
• Murray, J. R., R. Lohman and D. Sandwell (2013), Combining GPS and remotely sensed data to characterize time-varying crustal motion, EOS Trans. AGU, 94. SCEC Contribution 1801
• Spinler, J.C., Bennett, R.A., Anderson, M.L., McGill, S.F., Hreinsdottir, S., and McCallister, A., (2010), Present-day strain accumulation and slip rates associated with southern San Andreas and Eastern California shear zone faults: Journal of Geophysical Research, v. 115, B11407, doi:10.1029/2010JB007424, 29 p. SCEC Contribution 1405
• Thatcher, W., Y. Fialko, E. Hearn, and G. Hirth, Report on a 2013 Workshop on Ductile Rheology of the Southern California Lithosphere: Constraints from Deformation Modeling, Rock Mechanics, and Field Observations, May 1-2, 2013, USGS, Menlo Park, CA.
• Tong, X., B. Smith-Konter, and D. T. Sandwell (2014), Is there a discrepancy between geological and geodetic slip rates along the San Andreas Fault System?, J. Geophys. Res. Solid Earth, 119, doi:10.1002/2013JB010765. SCEC Contribution 2005
• Wei, M., Y. Kaneko, Y. Liu, and J. McGuire (2013), Episodic fault creep events in California controlled by shallow frictional heterogeneity, Nature Geoscience, 6, 566–570, doi:10.1038/ngeo1835. SCEC Contribution 1690