Research Interests
  • Space- and air-borne radar remote sensing
  • Multitemporal InSAR methods
  • Inverse theory
  • Numerical and analytical modeling of seismic and aseismic faulting processes
  • Volcanic source modeling
  • Groundwater hydro-geodesy
  • Sea level rise
  • Landslide
  • Planetary atmosphere

Active/Completed  Projects

NASA
  • Remote sensing of water mass budget variations in California.[Collaborative project: Prof.Werth (PI-ASU), Prof. Shirzaei (CoI-ASU), Prof. Fu (CoI-BGSU)]
  • Remote sensing of land subsidence and hydrological properties across Arizona. [NESSF fellowship, M. Miller]
  • Understanding and Predicting Coastal Sea Level Variability Around the United States. [Collaborative project: Prof. Shirzaei (PI-ASU), Dr. Argus (CoI-JPL), Prof. Chambers (CoI-USF)]
  • Mechanism of slow slip events on San Andreas fault: constraints from geodesy and seismology. [NESSF fellowship, M. Khoshmanesh]
NSF
  • Time-dependent creep model of the central creeping section of the San Andreas Fault from 21 years of InSAR, GPS and repeating earthquakes. [Prof. Shirzaei (PI)]
  • Origin of hydrologic responses to earthquakes: constraints from New Zealand, Taiwan, Chile, and the USA. [Collaborative project: Prof. Manga (PI-UCB), Prof. Shirzaei (CoI-ASU)]
  • Observations, Models and Mechanism of Spatiotemporal Interseismic Fault Creep in California. [Collaborative project: Prof. Shirzaei (PI-ASU), Dr. Taira (CoI-UCB), Dr. Thomas (CoI-UO)]
USGS
  • Application of InSAR and modeling to investigate time-dependent seismic hazard associated with waste water injection. [Dr. Shirzaei (PI)]

Multitemporal InSAR





Data from the Sentinel-1 synthetic aperture radar has already proven useful for investigating seismic and volcanic events since its launch on April 2014. The requirement of ultrahigh coregistration accuracy and the relatively short time of Sentinel-1 acquisitions make its application remain challenging for studying slow deformation processes, such as fault creep and land subsidence. Here, we advanced a multitemporal algorithm to analyze a set of 14 SAR images over the San Francisco Bay Area spanning 2015/03/01 to 2016/03/07. We applied an Enhanced Spectral Diversity algorithm to achieve the required coregistration accuracy. We obtain good interferometric coherence and find that the coregistration error is weakly correlated with the interferometric baselines. Following a thorough validation test, we used this data set to update our estimates of Hayward Fault creep rate, characterize subsidence along Bay Area coastlines and confirm recharge of the Santa Clara Valley aquifer system following an unprecedented 3-year drought. [Shirzaei et al. 2017 GRL]


 
 

Wavelet-based InSAR (WabInSAR) time series algorithm uses an improved filtering scheme that combines and inverts a large set of unwrapped interferograms to generate an accurate time series of the surface motion. This approach applies a variety of sophisticated wavelet based filters to estimate the interferometric phase noise and to reduce the effects of systematic and random artefacts, such as spatially correlated and temporal uncorrelated components of the atmospheric delay, and the digital elevation model and orbital errors. [Shirzaei 2013  JGR]







SAR satellites revisit the overlap zones of their adjacent tracks about twice as frequently than elsewhere. Due to datum and geometric differences between adjacent tracks and environmental artifacts, the task of combining these data sets is not trivial. A new physics-based approach is developed to unify the datums. The error due to the look angle difference is estimated and removed using a Kalman filter. The error associated with the atmospheric delay is reduced by applying wavelet based filters.
[Shirzaei 2015  G3]










Atmospheric delay is one of the major sources of error in repeat pass interferometry. A new approach is developed for correcting the topography-correlated components of this artifact. We use multiresolution wavelet analysis to identify the components of the unwrapped interferogram that correlate with topography. By using a forward wavelet transform we break down the digital elevation model and the unwrapped interferogram into their building blocks based on their frequency properties.  [Shirzaei & Burgmann 2012 GRL]







InSAR data are often obtained on the basis of repeated satellite acquisitions. Errors in the satellite orbit determination, however, propagate to the data analysis and may even entirely obscure the interpretation. In this work, wavelet multi-resolution analysis is employed to distinguish between the effects of orbital errors and other components (e.g., deformation signal).  Next, a robust regression approach is applied to estimate the effect of orbit errors as a ramp. [Shirzaei & Walter 2011 IEEE]

Inverse Theory

 
 

Random search approaches, such as Simulated Annealing (SA) and Genetic Algorithm (GA) are investigated and utilized in an iterated manner. The iterated approach helps to prevent GA in general and SA in particular from getting trapped in local minima, and it also increases redundancy for exploring the search space. A statistical competency test is applied for estimating the confidence interval of the inversion source parameters, considering their internal interaction through model, the effect of the model deficiency, as well as the observational error. [Shirzaei & Walter 2009 JGR]










A new approach for time-dependent, nonlinear inversion using a combination of a Genetic Algorithm (GA) and Kalman Filter (KF) is developed. The GA is used in the form presented by Shirzaei and Walter, [2009] and KF implementation now allows for the treatment of monitoring data as a full time series, rather than as single time steps. This approach provides a flexible tool for assessing unevenly sampled and heterogeneous time series data and explains the deformation field using time-consistent dislocation sources. [Shirzaei & Walter 2010 JGR]

Landslide

 

The detection and monitoring of gravity-driven volcano deformation is vital for understanding volcanic hazards, such as landslides, lateral blasts and debris avalanches. Although deformation has been detected at several large active volcanoes (e.g., Mt. Etna, Vesuvius, Kilauea), these systems also exhibit persistent magmatic activity, obscuring the gravity-driven signals of ground motion. In this study, we present a first InSAR deformation time series at the dormant Damavand volcano in northern Iran, over the period of 2003 through 2008. The high resolution data show a lateral extension of the volcano at the relative rate of up to ~6 mm/yr accompanied by a subsidence at the rate of up to ~5 mm/yr at the volcano summit. [Shirzaei et al. 2011 Geology]


Volcanic Source Modeling

 

A time-dependent source modeling technique is applied to InSAR data available between 1992 and 2008 from the Campi Flegrei volcano in Italy. Multiple episodes of linear velocity for reservoir pressure change is found associated with parabolic surface deformation at the volcano. This may be interpreted via differential equations as a linear flux to the shallow reservoir and provides new insight into how both the shallow and deep reservoirs communicate beneath Campi Flegrei. [Shirzaei & Walter 2010 JGR]







We show that during the 16-year records from 1992-2008, identified episodes of deformation occur that are in correlation. Albeit differences in the quantity of deformation, the sign, frequency and rate of pressure changes at reservoirs beneath Campi Flegrei and Vesuvius can be very similar, allowing to infer that pressure changes originating from a magmatic or tectonic source external to the shallow volcano magma plumbing systems is a likely cause. Such a fluidmechanical coupling sheds light on earlier episodes of correlated eruptions and deformations occurring during the historical roman times.  [Walter et al. 2014 JVGR]






The coupling of Mauna Loa and Kilauea volcanoes, Hawaii, has been debated for the past 100 years. The distinct composition of erupted materials at both volcanoes suggests that they draw on distinct magma reservoir in the mantle. In contrast, statistical analysis of the pattern of historic eruptions implies that Mauna Loa and Kilauea compete for magma supply.  Resolving this discrepancy, we present high-resolution spatiotemporal interferometric deformation maps using a well-populated catalogue of space-borne synthetic aperture radar data over Hawaii Island during 2003-2008. [Shirzaei et al 2013 GRL]






To explore the complex geometry and kinematics of the summit reservoir, a novel geometry-free time-dependent modeling scheme is applied to InSAR deformation time series at the Kilauea volcano.  The optimum model is characterized by a spheroidal and a tube-like zone of volume change beneath summit and the southwest rift zone at 2-3 km depth, respectively. To reduce the model dimension, we apply a Principal Component Analysis (PCA) scheme, which allows for the identification of independent reservoirs. The first 3 PCs, explaining 99% (63.8%, 28.5%, and 6.6%, respectively) of the model, include six independent reservoirs with a complex interaction suggested by temporal analysis. [Zhai & Shirzaei 2016 JGR]





The Lusi mud eruption, Indonesia, began in May 2006 and continues to the present. Previous analyses of surface deformation data suggested an exponential decay of the pressure in the mud source, but did not constrain the location, geometry and evolution of the possible source(s) of the erupting mud and fluids. To map the surface deformation, we employ multitemporal InSAR and analyze a well-populated data set acquired by ALOS L-band satellite between May 2006 and April 2011. We then apply a time-dependent inverse modeling scheme. Volume changes occur in two regions beneath Lusi, at 0.3-2.0 km and 3.5-4.75 km depth. The cumulative volume change within the shallow source is ~2-3 times larger than that of the deep source. The observation and model suggest that a shallow source plays a key role by supplying the erupting mud, but that additional fluids do ascend from depths >4 km on eruptive timescales. [Shirzaei et al 2015 GRL]








Faulting Processes

Spatial and temporal variations of aseismic fault creep represent important factors in realistic estimation of seismic hazard due to their influence on the size and recurrence interval of large earthquakes along partially coupled faults. To solve for a time-dependent model of creep on the Hayward fault, we invert 18 years of surface deformation data (1992 - 2010), obtained by interferometric processing of 52 and 50 synthetic aperture radar (SAR) images acquired by the ERS1/2 and ENVISAT satellites, respectively, and surface creep data obtained at more than 25 alinement and creepmeter stations. [Shirzaei & Burgmann 2013 JGR]

 










The Central segment of San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. However, observations of the creep rate obtained using small Characteristically Repeating Earthquakes (CREs) show pulses of creep along the CSAF, which may indicate spatially and temporally variable seismic hazard along the CSAF. Hre, we apply a time-dependent creep modeling approach, which combines InSAR surface deformation time series and observations of fault creep obtained from CREs. The resulting creep rate distribution implies a peak rate up to 32 mm/yr along the central part of the CSAF. Afterslip due to the 2004 Parkfield earthquake on the southeastern segment of the CSAF is also manifest in the model and there is clear evidence of creep pulsing along the strike and depth of the CSAF. The estimated annual rate of slip deficit accumulation is equivalent to a magnitude 5.6-5.7 earthquake. [Khoshmanesh et al. 2015 JGR]







Availability of dense continuous GPS and seismic monitoring networks provides a unique opportunity to study a variety of time-dependent processes associated with the 11 March 2011 Tohoku earthquake (Mw 9.0), such as afterslip deformation and postseismic relaxation. To this end we establish a time-dependent inversion scheme as a combination of L1-Norm minimization and Kalman filter. This framework allows inverting the time series of the surface deformation obtained from GPS networks constrained with direct observations of the fault slip obtained from repeating earthquakes. [Shirzaei et al. 2014 EPSL]









We show a rare example of aseismic response of a creeping fault to the earthquake cycle of a nearby megathrust. Interferometric synthetic aperture radar (InSAR) is used to detect and analyze shallow creep of two crustal faults at Mejilones Peninsula, Northern Chile, located in the hanging wall of the 2007 Mw7.7 Tocopilla subduction earthquake.
[Shirzaei et al. 2012 EPSL]









The Hilina Fault System (HFS) is located on the south flank of Kilauea volcano and is thought to represent the surface expression of an unstable edifice sector that is active during seismic events such as the 1975 Kalapana earthquake. Despite its potential for hazardous landsliding and associated tsunamis, no fault activity has yet been detected by means of modern geodetic methods since the 1975 earthquake. Using wavelet transforms in a statistical framework, we jointly analyze InSAR and continuous GPS deformation data from 2003 to 2010 to resolve a subtle deformation signal about the HFS normal fault scarps. [Shirzaei et al. 2013 EPSL]





Models of Himalayan neotectonics generally attribute most active mountain building in the range to slip on the Himalayan Sole Thrust (HST), which accommodates underthrusting of the Indian Plate beneath Tibet. However, the geometry of the HST and thus how slip along it causes uplift of the High Himalaya are unclear. We show that the 2015 Gorkha earthquake sequence adds important clarity to the architecture of the HST, suggesting that the canonical view of how the Himalaya grow may require revision. Inversion of surface deformation patterns for the event, as revealed by InSAR and GPS data, implies that the HST extends as a planar gently-dipping fault surface from near the Himalayan thrust front northward for at least 100 km, well north of the main physiographic transition demarcating the southern flank of the High Himalaya, implying that building of the high range cannot be attributed solely to slip along HST over a steep ramp, as has commonly been inferred.  [Whipple et al. 2016 NGeo]


Time-dependent Seismic Hazards

 

The probability of large seismic events on a particular fault segment may vary due to external stress changes imparted by nearby deformation events, including other earthquakes and aseismic processes, such as fault creep and postseismic relaxation. We use surface deformation data to investigate the kinematics of fault creep on the northern HF and its relation to two seismic clusters in October 2011 and March 2012, and an Mw4.2 event in July 2007. We estimate that the 1-day probability of a large event on the HF only increased by up to 0.18% and 0.05% due to the static stress increase and stressing rate change by the 2011 and 2012 clusters. For the July 2007 south Oakland event (Mw4.2) the estimated increase of short-term probabilities is 50%, highlighting the importance of short-term probability changes due to transient stress changes. [Shirzaei et al. 2013 EPSL]

 


Fluid Injection

 

Observations that unequivocally link seismicity and wastewater injection are scarce. Here we show that wastewater injection in eastern Texas causes uplift, detectable using radar interferometric data to > 8 km from the wells. Using measured uplift, reported injection data, and a poroelastic model, we compute the crustal strain and pore pressure. We infer that a > 1 MPa increase in pore pressure in rocks with low compressibility triggers earthquakes including the Mw4.8, 17 May 2012 event, the largest earthquake recorded in east Texas. Seismic activity increased even while injection rates declined owing to diffusion of pore pressure from earlier periods with higher injection rates. Induced seismicity potential is suppressed where tight confining formations prevent pore pressure from propagating into crystalline basement rocks. [Shirzaei et al. 2016 Science]