Auxiliary Material for
Breaking the Oceanic Lithosphere of a Subducting Slab: The 2013 Khash, Iran Earthquake
W.D. Barnhart (1)
G.P. Hayes (1)
S.V. Samsonov (2)
E.J. Fielding (3)
L.E. Seidman (1)
Affiliations:
1: U.S. Geological Survey National Earthquake Information Center
2: Canada Centre for Remote Sensing
3: Jet Propulsion Laboratory
Introduction:
This supplemental material includes (1) document with supplemental methods, (6) figures, (2) tables, and
(1) supplemental data set.
Supplemental Methods (2013GL057408-textA01.txt): Methods used to process Radarsat-2 interferograms,
generate finite fault slip models from both interferograms and teleseismic observations, and generation of
the Makran slab model.
Supplemental Table 1 (2013GL057408-textA02.txt): Radarsat-2 interferogram pair information for
coseismic scenes used in this study. Date1/Date2: Scene acquisition dates (yyyy.mm.dd) and orbit ID (in
parentheses), # Frames: number of individual frames included in each interferogram. Beam: Satellite
acquisition mode (see supplemental methods), Bperp: Perpendicular baseline between scenes, in meters,
Incidence: Satellite incidence angle, Heading: Satellite heading angle. All scenes are ascending viewing
geometries. *- Interferogram shown in Figure 2. ^- Interferogram shown in Figure 1. All spatial extents are
shown in figure 1. All individual frames have spatial dimensions of 90x50 km (range x azimuth).
Supplemental Table 2 (2013GL057408-textA03.docx): Fault model parameters and slip modeling results
from InSAR and teleseismic observations. Lon/Lat: top corners of the fault models. zc: depth range of
largest slip values, z: depth range of all significant slip (>0.5m), strike/dip/rake: orientation of fault plane
and slip direction (in Global CMT convention), L: fault model length, W: fault model width, Mw: inferred
moment magnitude for each slip distribution. *- indicates fixed value, ^-indicates mean of free rake
inversion, $-slip distributions shown in Figures 2 and 3 and preferred models. Values in parentheses
indicate 1-sigma uncertainty bounds from Monte Carlo statistical analysis from 100 iterations of the
Neighborhood Algorithm. ID: SP – single patch (and dip direction), DS – distributed slip (and dip
direction), S-Free – teleseismic, location unconstrained a-priori, S-Fixed – teleseismic, fault model is
coplanar with DS-North. Best-fit models are chosen through a combined L1-L2 norm assessment
(teleseismic) or the jRi criterion (InSAR), see supplemental methods.
Supplemental Data (2013GL057408-textA04.txt): Resampled coseismic interferograms used to invert for
finite fault geometry and slip. File includes lon/lat of resampled data points, LOS displacement (in meters),
and the three components of the look vector for each point. Point locations are show in Figure S1.
Supplemental Figure 1 (2013GL057408-pA01.tif): Interferograms used in this study (Table S1). Column 1:
Unwrapped interferograms with an initial quadratic ramp removed. Column 2: Resampled interferograms.
Points indicate the location of resampled data points. Column 3: Predicted surface displacements from the
preferred model with simultaneous removal of a linear ramp (Figure 2b, DS-North in Table S2). Column 4:
Residuals resulting from the best-fit north dipping focal plane (Figure 2b). Column 5: Residuals resulting
from the best-fit south dipping focal plane with geometry fixed to the USGS W-phase solution (strike=87,
dip=36) (Figure S2a, Table S2:DS-South). Colors are line-of-sight displacement in cm, negative indicates
motion away from the satellite. Resampled data is available in the auxiliary data set. Interferograms
overlain on shaded SRTM DEM [Farr et al., 2007].
Supplemental Figure 2 (2013GL057408-pA02.tif): a) Best-fit slip distribution for a south dipping focal
plane with fixed strike and dip according to the USGS W-phase solution. To obtain the fault location and
rake, we fix strike and dip, and invert for all other unknowns using the Neighborhood Algorithm. Then we
solve for distributed slip using the method described in the supplemental methods. Residuals to the model
fit are shown in Supplemental Figure 1. b) Error analysis of the north dipping focal plane (Figure 2b)
inverted from InSAR. Depth profiles of best fit InSAR slip distribution (black line), best fit teleseismic slip
distribution (red line), and models resulting from Monte Carlo tests (thin gray lines) with associated 1sigma error bounds (heavy gray lines).
Supplemental Figure 3 (2013GL057408-pA03.tif): Finite fault modeling for the 04-06-13 Mw 7.7 Khash
earthquake based on the NEIC epicenter location. a) Source time function for our best-fitting single-plane
finite fault model, prior to adjustments using InSAR data. b) Map view of the slip distribution, shown in
cross-section in (c). The star represents the preferred hypocenter. In (b), slip is contoured in 1 m
increments. In (c), contours represent the moveout of the rupture front, plotted every 5 s. Background
bathymetric data in (b) is taken from the ETOPO1 elevation grid [Amante and Eakins, 2009]. Model
corresponds to ID S-Free, Supplemental Table 2.
Supplemental Figure 4 (2013GL057408-pA04.tif): Representative waveform fits for the finite fault model
(Figure 2a, S5a, Table S2 S-Fixed). In (a) we show teleseismic P- and SH-wave displacement waveforms;
(b) shows surface wave fits. Data and synthetics are shown in black and red, respectively. Numbers at the
beginning of each record represent distance (bottom) and azimuth (top) to station, while numbers at the end
of each record represent the peak amplitude of the data. Body wave fits are identical to those shown in
Figure 2c. Globe shows the distribution of seismometers used relative to the event epicenter.
Supplemental Figure 5 (2013GL057408-pA05.tif): Adjusted finite fault model and resolution analyses. In
(a), we show our favored finite fault model for the Khash earthquake, adjusted from Figure S1 using InSAR
data to infer a new hypocenter, and to constrain shallow slip to zero (Table S2, S-Fixed). In (b) we show
our favored average model from a bootstrap analysis incorporating 125 individual inversions, with variable
Vr (Shown in Figure 2a). The inset (c) shows the collection of source time functions derived from each
inversion (gray lines), superimposed with the average solution (black line). The source time function from
the single inversion in (a) is shown in red. Model fits are shown in Figure 2c and Supplemental Figure 4.
Supplemental Figure 6 (2013GL057408-pA06.tif): a) Broadband depth modeling misfit function for the
Khash earthquake. Figure shows the misfit between broadband teleseismic body-wave data and Hudson
synthetic seismograms [Hudson, 1969] computed using the fit function of Herrmann et al. [2011], and
scaled relative to the best-fitting solution (80 km depth and 18.6 source duration). This method models
body-wave depth-phases and source duration with symmetric triangular source time functions, constructed
using the ak135 velocity model [Kennett et al., 1995]. B) Comparison of RMS misfit for teleseismic
waveform models (red) with hypocentral depth constrained at 5km increments between 35 and 80km. C)
Teleseismic slip distributions for models with a hypocenter incrementally increased from 35km to 80km.
Star in the slip distributions indicates the location of the hypocenter (starting location of the slip model).
All units are in meters. In general, the bulk characteristics of the slip distribution do not change with
changing hypocenter except for the large magnitude of shallow slip that appears for hypocenters shallower
than 55 km. This region of slip is unconstrained by waveforms and appears because of the forced
hypocentral depth – indicating these are unreasonable depths for the hypocenter.
Supplemental Figure 7 (2013GL057408-pA07.tif): Maps showing inferred depth to the top of the slab and
slab dip for the Makran. See supplemental methods for description of derivation of geometries. Images
overlain on ETOPO1 elevation grid [Amante and Eakins, 2009].
Supplemental Figure 8 (2013GL057408-pA08.tif): Model misfits for the 3 resampled interferograms
(Figure S1, column 2) for a range of centroid depths. To invert for slip, we fix the center of the fault plane
at various depths (indicated by depth), then invert for strike, dip, rake, location, and dimensions of a single
fault patch. Values in parentheses are best-fit strike/dip/rake/Mw resulting from each model. Models are
allowed to explore the full range of orientations (strike=0-360, dip=0-90). The misfits indicate both that the
signal is fit best by a deeper (>20km) source and a single fault patch is insufficient to model the
displacements. Reported values are LOS displacements in centimeters.
Supplemental Figure 9 (2013GL057408-pA09.tif): Results of InSAR inversions where the north-dipping
focal plane (Figure 2b) is restricted to narrow depth ranges (35 km) both above and below the slab. Slip
distributions and model residuals are shown for each inversion.
Supplemental Figure 10 (2013GL057408-pA10.tif): Teleseismic slip distribution (a) and source time
function (b) for the south-dipping focal plane constrained by the W-phase centroid moment tensor. c) Slip
distribution shown in map view with contours of the slab top. Slip propagates higher than the slab top,
implying rupture would have to propagate into the overriding plate. Observations (black) and synthetic
(red) for body (d) and surface waveforms (e). Figure annotations same as Figure S4.
References:
Amante, C., and B. W. Eakins (2009), ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data
Sources and Analysis.,
Farr, T. G. et al. (2007), The Shuttle Radar Topography Mission, Rev. Geophys., 45(2), n/a–n/a,
doi:10.1029/2005RG000183.
Herrmann, R. B., H. Benz, and C. J. Ammon (2011), Monitoring the Earthquake Source Process in North
America, Bull. Seismol. Soc. Am., 101(6), 2609–2625, doi:10.1785/0120110095.
Hudson, J. A. (1969), A Quantitative Evaluation of Seismic Signals at Teleseismic Distances—I Radiation
from Point Sources, Geophys. J. R. Astron. Soc., 18(3), 233–249, doi:10.1111/j.1365246X.1969.tb03567.x.
Kennett, B. L. N., E. R. Engdahl, and R. Buland (1995), Constraints on seismic velocities in the Earth from
traveltimes, Geophys. J. Int., 122(1), 108–124, doi:10.1111/j.1365-246X.1995.tb03540.x.