Research

The current global projections of future sea level rise are the basis for developing inundation hazard maps. However, contributions from spatially variable coastal subsidence have generally not been considered in these projections. Here, we use SAR interferometric measurements and GNSS data to show subsidence rates of less than 2 mm/yr along the majority of coastal areas along San Francisco Bay. However, rates exceed 10 mm/yr in some areas underlain by compacting artificial landfill and Holocene mud deposits. The maps estimating 100-year inundation hazards solely based on the projection of sea level rise from various emission scenarios underestimate the area at risk of flooding by 3.7% - 90.9%, compared with revised maps that account for the contribution of local land subsidence. Given ongoing land subsidence, we project that an area of 125 km2 – 429 km2 will be vulnerable to inundation, as opposed to 51 km2 – 413 km2 considering sea level rise alone. [Shirzaei & Burgmann 2018 Science Ad.]

The accelerated rate of decline in groundwater levels across California’s Central Valley results from over-drafting and low rates of natural recharge and is exacerbated by droughts. The lack of observations with adequate spatiotemporal resolution to constrain the evolution of groundwater resources poses serious challenges to water management efforts. Here, we present SAR interferometric measurements of high-resolution vertical land motion across the valley, revealing multiscale patterns of aquifer hydrogeological properties and groundwater storage change. Investigating the depletion and degradation of the aquifer-system during 2007 – 2010, when the entire valley experienced a severe drought, we find that ~2% of total aquifer-system storage was permanently lost, owing to irreversible compaction of the system. Over this period, the seasonal groundwater storage change amplitude of 10.11 ± 2.5 km3 modulates a long term groundwater storage decline of 21.32 ± 7.2 km3. Estimates for sub-basins show more complex patterns, most likely associated with local hydrogeology, recharge, demand and underground flow. Presented measurements of aquifer-system compaction provide a more complete understanding of groundwater dynamics and can potentially be used to improve water security. [Ojha et al. 2018 WRR]

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] 

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 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.

Random search approaches, such as Simulated Annealing (SA) and Genetic Algorithm (GA), are investigated and utilized in an iterated manner. The iterated approach helps 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 a model, the effect of the model deficiency, and the observational error.

The detection and monitoring of gravity-driven volcano deformation are 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 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 subsidence at the rate of up to ~5 mm/yr at the volcano summit.

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] 

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]