Y. N. Lin

A multiscale approach to estimating topographically correlated propagation delays in radar interferograms

When targeting small amplitude surface deformation, using repeat orbit Interferometric Synthetic Aperture Radar (InSAR) observations can be plagued by propagation delays, some of which correlate with topographic variations. These topographically-correlated delays result from temporal variations in vertical stratification of the troposphere. An approximate model assuming a linear relationship between topography and interferometric phase has been used to correct observations with success in a few studies. Here, we present a robust approach to estimating the transfer function, K, between topography and phase that is relatively insensitive to confounding processes (earthquake deformation, phase ramps from orbital errors, tidal loading, etc.). Our approach takes advantage of a multiscale perspective by using a band-pass decomposition of both topography and observed phase. This decomposition into several spatial scales allows us to determine the bands wherein correlation between topography and phase is significant and stable. When possible, our approach also takes advantage of any inherent redundancy provided by multiple interferograms constructed with common scenes. We define a unique set of component time intervals for a given suite of interferometric pairs. We estimate an internally consistent transfer function for each component time interval, which can then be recombined to correct any arbitrary interferometric pair. We demonstrate our approach on a synthetic example and on data from two locations: Long Valley Caldera, California, which experienced prolonged periods of surface deformation from pressurization of a deep magma chamber, and one coseismic interferogram from the 2007 Mw 7.8 Tocapilla earthquake in northern Chile. In both examples, the corrected interferograms show improvements in regions of high relief, independent of whether or not we pre-correct the data for a source model. We believe that most of the remaining signals are predominately due to heterogeneous water vapor distribution that requires more sophisticated correction methods than those described here.

Multiscale InSAR Time Series (MInTS) analysis of surface deformation

[1] We present a new approach to extracting spatially and temporally continuous ground deformation fields from interferometric synthetic aperture radar (InSAR) data. We focus on unwrapped interferograms from a single viewing geometry, estimating ground deformation along the line-of-sight. Our approach is based on a wavelet decomposition in space and a general parametrization in time. We refer to this approach as MInTS (Multiscale InSAR Time Series). The wavelet decomposition efficiently deals with commonly seen spatial covariances in repeat-pass InSAR measurements, since the coefficients of the wavelets are essentially spatially uncorrelated. Our time-dependent parametrization is capable of capturing both recognized and unrecognized processes, and is not arbitrarily tied to the times of the SAR acquisitions. We estimate deformation in the wavelet-domain, using a cross-validated, regularized least squares inversion. We include a model-resolution-based regularization, in order to more heavily damp the model during periods of sparse SAR acquisitions, compared to during times of dense acquisitions. To illustrate the application of MInTS, we consider a catalog of 92 ERS and Envisat interferograms, spanning 16 years, in the Long Valley caldera, CA, region. MInTS analysis captures the ground deformation with high spatial density over the Long Valley region.

New Radar Interferometric Time Series Analysis Toolbox Released

Interferometric synthetic aperture radar (InSAR) has become an important geodetic tool for measuring deformation of Earth’s surface due to various geophysical phenomena, including slip on earthquake faults, subsurface migration of magma, slow‐moving landslides, movement of shallow crustal fluids (e.g., water and oil), and glacier flow. Airborne and spaceborne synthetic aperture radar (SAR) instruments transmit microwaves toward Earth’s surface and detect the returning reflected waves. The phase of the returned wave depends on the distance between the satellite and the surface, but it is also altered by atmospheric and other effects. InSAR provides measurements of surface deformation by combining amplitude and phase information from two SAR images of the same location taken at different times to create an interferogram. Several existing open‐source analysis tools [Rosen et al., 2004; Rosen et al., 2011; Kampes et al., 2003 ; Sandwell et al., 2011] enable scientists to exploit observations from radar satellites acquired at two different epochs to produce a surface displacement map.

PCAIM joint inversion of InSAR and ground-based geodetic time series: Application to monitoring magmatic inflation beneath the Long Valley Caldera

This study demonstrates the interest of using a Principal Component Analysis-based Inversion Method (PCAIM) to analyze jointly InSAR and ground-based geodetic time series of crustal deformation. A major advantage of this approach is that the InSAR tropospheric biases are naturally filtered out provided they do not introduce correlated or high amplitude noise in the input times series. This approach yields source models which are well-constrained both in time and space due to the temporal resolution of the ground-based geodetic data and the spatial resolution of the InSAR data. The technique is computationally inexpensive allowing for the inversion of large datasets. To demonstrate the performance of this approach, we apply it to the 1997–98 magmatic inflation event in the Long Valley Caldera, California.

Shallow Rupture of the 2011 Tarlay Earthquake (Mw 6.8), Eastern Myanmar

We use L‐band Advanced Land Observation Satellite PALSAR data to infer the distribution of subsurface fault slip during the Tarlay earthquake (M_w 6.8) in eastern Myanmar. We find the total length of surface rupture is approximately 30 km, with nearly 2 m maximum surface offset along the westernmost section of the Nam Ma fault (the Tarlay segment). Finite‐fault inversions constrained by Interferometric Synthetic Aperture Radar (InSAR) and pixel‐tracking data suggest that fault slip is concentrated within the upper 10 km of the crust. Maximum slip exceeds 4 m at a depth between 3 and 5 km. Comparison between field measurements and near‐fault deformation obtained from the InSAR range‐offset result suggests about 10%–80% of displacement occurred within a 1 km wide zone off the main surface fault trace. This off‐fault deformation may explain the shallow slip deficit that we observed during this earthquake. We estimate a recurrence interval for Tarlay‐like events to be 1600–6500 yrs at this section of the Nam Ma fault. A detailed paleoseismological study is essential to clarify the slip behavior and the earthquake recurrence interval of the Nam Ma fault.

Submarine landslides along the Malacca Strait-Mergui Basin shelf margin: Insights from sequence-stratigraphic analysis

The enormously destructive tsunami of December 2004, caused by sudden motion of the Sunda megathrust beneath the Indian Ocean, raised concerns about tectonically induced tsunami worldwide. Submarine landslides may also trigger dangerous tsunami. However, the potential and repeat time for such events is in most places poorly known due to inadequate exploration of the sea floor and age constraints. The high sediment flux and tectonic subsidence rate of the Malacca Strait-Mergui Basin shelf margin NE of northernmost Sumatra provide a favorable environment to generate and preserve submarine landslides. From ten seismic reflection profiles acquired in 2006, we identify three sediment packages that exhibit sliding characteristics such as headscarps, distorted beds and debris-toe structures. We assign lowstand marine isotope stages to the paleo-shoreline indicators observed in the profiles. We then determine the ages of these submarine landslides as 20–30 ka, 342–364 ka and 435–480 ka by the paleo-shoreline indicators that bound the top and bottom of the slide bodies. This sequence-stratigraphic approach shows that these events occurred near times of sea-level lowstands, which implies that a large amount of direct sediment influx during glacial periods is an essential precondition for basin-margin submarine landsliding. Spatiotemporal variations of sediment input due to lobe switching or Asian monsoon intensity changes also control basin-margin instability. Because we are currently at a highstand stage, and sediment flux to the continental margin is relatively small, so the chance of having a repeat submarine landslide and landslide tsunami along this basin-margin is low.