Research

Research Topics

My research interests cover a broad range of tectonic and non-tectonic processes that can be detected using Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) data.  See below for more information on my research on the following topics: 

Aseismic Slip in Fault Zones

Figure: Geodetic inversion results (top) and InSAR data (bottom) near North Brawley, CA. Typical of earthquake swarms in the BSZ, the 2012 Brawley sequence produced a combination of seismic and aseismic slip. 

Seismic and Aseismic Slip in the Brawley Seismic Zone

The Brawley Seismic Zone (BSZ), at the southern end of the San Andreas Fault system, hosts frequent seismic swarms including the 2012 Brawley swarm that produced two M5 earthquakes. Aseismic slip is known to accompany some of the seismic swarms in the BSZ. In this project, we consider a large collection of GNSS and InSAR data to constrain the deformation from seismic and aseismic slip across 2009-2019 at the North Brawley Geothermal Field. The long time series displays evidence for both aseismic slip and poroelastic deformation at different times, allowing us to probe the conditions under which slip occurs in the BSZ.

More info: Materna, K., A. Barbour, J. Jiang, and M. Eneva (2022), Detection of aseismic slip and poroelastic reservoir deformation at the North Brawley Geothermal Field from 2009-2019, Journal of Geophysical Research: Solid Earth, 127, doi:10.1029/2021JB023335.

Figure: Repeating earthquake families offshore CA near the MTJ.

Repeating Earthquakes at the Mendocino Triple Junction

The Mendocino Triple Junction (MTJ) is one of the most seismically active regions of California, and provides a unique opportunity to study active oceanic transform faults close to land. In this project, we study characteristically repeating earthquakes on the Mendocino Transform Fault near the MTJ. We use these sequences of repeating earthquakes to determine fault creep rates and a time series of slip. We find that in a few places, up to 50% of the slip budget is accommodated aseismically through creep. This result can be used to create more realistic models of interseismic strain accumulation, earthquake interactions, and stress loading in the MTJ.

More info: Materna, K., T. Taira, and R. Bürgmann (2018), Aseismic transform fault slip from characteristically repeating earthquakes at the Mendocino Triple Junction, Geophysical Research Letters, 45, doi: 10.1002/2017GL075899.

Plate Boundary Deformation at the Mendocino Triple Junction

Interseismic fault loading near MTJ constrained by geodetic data

The MTJ contains many faults with poorly known slip rates but the potential for present-day seismic activity.  To better understand these faults, we use a viscoelastic earthquake cycle approach to model the three-component interseismic velocity field from GNSS, leveling, and tide gage measurements. This work aims to constrain the present-day slip rates on the Little Salmon fault and surrounding faults using horizontal and vertical interseismic velocity data combined with a modeling approach that has not previously been applied to this seismically active area. 

More info: Materna, K., J. Murray, F. Pollitz, and J. Patton (2023), Slip deficit rates on southern Cascadia faults resolved with viscoelastic earthquake cycle modeling of geodetic deformation, BSSA, doi:10.1785/0120230007.

MTJ velocity changes, c/o Kathryn Materna

GNSS Velocity Changes at the Mendocino Triple Junction (MTJ)

In southern Cascadia, GNSS measurements spanning about 15 years reveal steady deformation due to coupling on the Cascadia megathrust punctuated by transient deformation from large earthquakes and episodic tremor and slip events. However, near the MTJ, time-variable GNSS deformation suggests additional processes. After correcting for earthquakes and seasonal loading, we find that several dozen GNSS time series show spatially coherent east-west velocity changes of ~2 mm/yr, and that these changes coincide in time with regional M>6.5 earthquakes. After examining a range of other hypotheses, we consider dynamically triggered changes in megathrust coupling most likely to explain the data. This finding suggests that plate interface coupling may be variable with time during the interseismic period, which has implications for megathrust coupling models.

More info: Materna, K., N. Bartlow, A. Wech, C. Williams, and R. Bürgmann (2019), Dynamically Triggered Changes of Plate Interface Coupling in Southern Cascadia, Geophysical Research Letters, doi:10.1029/2019GL084395.

Interseismic Strain Accumulation

Figure: Mean strain rate field and epistemic uncertainty on the strain rate field calculated from five published strain rate techniques. 

Epistemic uncertainty in strain rate calculations

Computing strain rate from geodetic velocities requires modeling choices made by the analyst to account for discrete and non-uniformly-spaced data. In this study, we quantitatively analyze the impact of modeling choices on the resulting strain rate field through comparing the results of five published strain rate modeling techniques applied to the same GNSS velocity dataset. We find that epistemic uncertainties due to modeling choices can be large even in areas with high station density, such as Parkfield CA, especially if the changing inter-station spacing is not properly accounted for.  Our results have implications for the uncertainty of seismic moment calculations that rely upon strain rate modeling as inputs.

More info: Maurer, J., and K. Materna (2023), Quantification of geodetic strain rate uncertainties and implications for seismic hazard estimates, Geophysical Journal International, 234, 3, p. 2128-2142, doi: 10.1093/gji/ggad191. 

Fault Zone Mechanical Properties

SF Bay Area GNSS velocities, c/o Kathryn Materna

Compliant Fault Zones in the San Francisco Bay Area

Many mature faults are characterized by damage zones that can extend hundreds of meters to several kilometers from the fault trace. These damage zones can impact the interseismic and co-seismic behavior of faults. On the San Andreas Fault, a major source of seismic hazard in the San Francisco Bay Area, we use dense networks of survey-mode and continuous GPS observations to place constraints on the mechanical properties of the fault zone. In particular, we investigate the contribution of a damage-zone structure called a compliant fault zone (CFZ) to the interseismic deformation field.

More Info: Materna, K. and R. Bürgmann (2016), Contrasts in compliant fault zone properties inferred from geodetic measurements in the San Francisco Bay Area, Journal of Geophysical Research: Solid Earth, 121, doi: 10.1002/2016JB013243. 

Figure: Left) Tectonic setting of the 2017 M6.5 Botswana earthquake. Right) InSAR displacement data spanning the earthquake. 

Coseismic deformation of the M6.5 Moijabana, Botswana earthquake

On April 3, 2017, an unusual earthquake occurred in a region of Botswana with little active seismicity and no active faults. In order to investigate the causative fault, we study the event's source from a joint inversion of Sentinel-1 InSAR and teleseismic body waves. We find that the joint inversion places stronger constraints on the source fault's orientation and depth than the InSAR inversion alone. It is important to study intraplate events such as this one, as they provide rare opportunities to understand slow deformation deep in the crust and away from plate boundaries.

More info: Materna, K., S. Wei, X. Wang, L. Heng, T. Wang, W. Chen, R. Salman, and R. Bürgmann (2019), Source characteristics of the 2017 Mw 6.4 Moijabana, Botswana earthquake, a rare lower-crustal event within an ancient zone of weakness, Earth and Planetary Science Letters, 506, doi:10.1016/j.epsl/2018.11.007.

Hydrological Loading Processes

Figure: Example GNSS time series from Myanmar, India, Bhutan, and Bangladesh. 

Hydrological Loading in Myanmar and S.E. Asia

In this project, in collaboration with researchers at the Earth Observatory of Singapore, we investigate annual signals in vertical GNSS time series in Myanmar, India, Bangladesh, and Bhutan. We produce time-dependent models of elastic hydrological loading from GRACE gravity measurements and other models, and compare with observed GNSS. These types of corrections can be used to reduce scatter in vertical measurements, improving our ability to detect tectonic signals.

More info: Materna, K., L. Feng, E. Lindsey, E. Hill, A. Ahsan, A. K. M. Alam, K. Oo, O. Than, T. Aung, S. Khaing, and R. Bürgmann (2021), GNSS characterization of hydrological loading in South and Southeast Asia, Geophysical Journal International, 224, doi:10.1093/gji/ggaa500. 

Figure: Daily water storage from inversion of GNSS displacements, and daily precipitation amounts from satellite measurements.

Transient Loading following Hurricane Harvey

Hurricane Harvey made landfall on the coast of Texas in August 2017 and brought with it historic quantities of rain. In this project, we determine the amount of precipitation (95 km^3) and how long it remained in the hydrological system (about 5 weeks) through modeling the elastic loading produced on the Earth's surface and measured by continuous GNSS stations. This research advances our ability to monitor the hydrological system at high spatial and temporal resolution using GNSS data.

More info: Milliner, C., K. Materna, R. Bürgmann, Y. Fu, A. Moore, D. Bekaert, S. Adhikari, and D. Argus (2018), Tracking the weight of Hurricane Harvey’s stormwater using GPS data, Science Advances, 4, eaau2477.