Global compilation of interferometric synthetic aperture radar earthquake source models: 2. Effects of 3-D Earth structure

Abstract

[1] We carry out long-period surface wave centroid moment tensor (CMT) inversions using various global tomographic models and two different forward modeling techniques for 32 large earthquakes previously studied using interferometric synthetic aperture radar (InSAR) data. Since InSAR methods provide an alternative and independent way of locating and characterizing shallow continental earthquakes, comparisons of our source parameters with those from InSAR are a novel way to assess limitations in the InSAR models as well as the effects of inaccurate wave propagation formulations and/or 3-D Earth structure on earthquake source determinations. We show that comparing InSAR results with our seismic solutions is valuable to identify inaccuracies in the earthquake slip distribution retrieved using InSAR. Moreover, we find that using more accurate formulations, together with the best fitting Earth models, substantially reduces biases and differences between moment magnitude and fault strike determined using InSAR and seismic data. As expected for long-period surface wave source inversions for shallow earthquakes, the fault dip and rake angles are difficult to constrain, but we show that when using the best fitting Earth models, differences to InSAR estimates are reduced. Moreover, spurious deviations from a pure double-couple earthquake mechanism are on average smaller for the best fitting Earth models and the more accurate formulation of wave propagation. There are large differences between InSAR epicentral locations and those obtained in this study and, on average, no clear improvements to the Global CMT locations are achieved. This suggests that higher-resolution Earth models are necessary to further refine long-period CMT epicentral locations.Citation: Ferreira, A. M. G., J. Weston, and G. J. Funning (2011), Global compilation of interferometric synthetic aperture radar earthquake source models: 2. Effects of 3-D Earth structure,

Active accommodation of plate convergence in Southern Iran: Earthquake locations, triggered aseismic slip, and regional strain rates

“…The location migrates approximately along the NE‐SW azimuth, indicating that the distribution of seismometers may contribute, in part, to the observed bias (Figure ). We infer that the remaining misfit is likely due to the neglect of three‐dimensional variations in seismic velocity in our modeling, as postulated by others [ Syracuse and Abers , ; Ferreira et al ., ; Myers et al ., ; Weston et al ., ].…”

“…Here we compare our catalog of earthquake locations inferred from InSAR to global catalogs (GCMT, National Earthquake Information Center (NEIC), and ISC) to explore if systematic epicentral mislocations exist. For many regions, offsets between InSAR and teleseismic epicenter locations appear random [e.g., Elliott et al ., ; Weston et al ., ], and mislocations can be attributed to trade offs between epicenter, depth, and source function or random velocity structure errors [ Ferreira et al ., ; Devlin et al ., ]. Regions where systematic mislocations exist help to identify major structures, such as subducting slabs, that must be accounted for with more accurate velocity models to correctly locate earthquakes [e.g., Syracuse and Abers , ].…”

“…While hypocentral locations from seismic waveforms are often the primary observation used to identify regions of elevated seismogenic hazard, to quantify the seismogenic thickness of the crust, and to define geometries and locations of major faults, geodetic observations such as interferometric synthetic aperture radar (InSAR) can provide independent, spatially dense observations of earthquake ground displacements over broad areas (>100 km) [e.g., Bürgmann et al, 2000;Pritchard et al, 2002;Barnhart et al, 2011;Devlin et al, 2012]. Catalogs of events observed with InSAR can allow identification of systematic location biases in global seismic catalogs [e.g., Ferreira et al, 2011;Devlin et al, 2012] and provide important constraints on the precision of seismically derived source locations. In regions where substantial aseismic slip accompanies earthquake ruptures [Langbein et al, 2006;Lohman and McGuire, 2007;Barnhart and Lohman, 2013], InSAR observations can illuminate how overall strain accommodation varies across the plate boundary and throughout the seismic cycle.…”

Breaking the oceanic lithosphere of a subducting slab: The 2013 Khash, Iran earthquake

“…This results (Figure b) in a nearly identical spatial distribution of slip to the original seismic model (Figure S3) while improving the fit of the waveforms. The ~30 km mislocation of the NEIC solution is not unexpected, given the uncertainties in teleseismic locations and likely results from unmodeled 3‐D velocity structure [e.g., Ferreira et al ., ; Myers et al ., ].…”

Global Earthquake Response with Imaging Geodesy: Recent Examples from the USGS NEIC

“…The nature of contributions of geodesy have varied broadly, from providing independent verification of an earthquake location or teleseismic finite fault model, to independently acting as the For smaller earthquakes (<M w 6-7), geodetic observations can provide a location of the earthquake to within the bounds of a source model inverted from the observations, including a depth range estimate, that supplements seismological source estimates. This capability is particularly important in regions where earthquakes are mislocated or where focal depths are difficult to constrain due to limited regional seismic observations [38][39][40][41].…”