Journal of Geophysical Research Solid Earth
Supporting Information for
Fault-Slip Source Models for the 2014 Mw 6.9 Samothraki-Gökçeada Earthquake (North
Aegean Trough) Combining Geodetic and Seismological Observations
Vasso Saltogianni (1), Michail Gianniou (2), Tuncay Taymaz (3), Seda Yolsal-Çevikbilen (3),
and Stathis Stiros (1)*
(1) Department of Civil Engineering, University of Patras, Patras, Greece,
(2) National Cadastre and Mapping Agency SA, Athens, Greece,
(3) Department of Geophysical Engineering, The Faculty of Mines, İstanbul Technical University, İTÜ Maslak
Campus, 34469, Sarıyer, İstanbul, Turkey
*corresponding author: Laboratory of Geodesy and Geodetic Applications, Dept. of Civil Engineering, Patras
University, Rio 26500, Greece, tel: +30 2610 996511, fax: +30 2610 997877, email: stiros@upatras.gr
Contents of this file
Text S1 to S2
Figures S1 to S7
Tables S1 to S3
Additional Supporting Information (Files uploaded separately)
Captions for Movie S1
Introduction
This file contains additional Text, Figures and Tables supporting the main article. In particular
Text S1: Detailed description of the analysis of the seismological data.
Text S2: Details of geodetic data and validation of the PPP solutions.
Figure S1: Location map of the stations used in seismological analysis.
Figure S2: Distributions of P- wave first motion polarities of the May 24, 2014 earthquake.
Figure S3: Comparison of the source parameters of the May 24, 2014 earthquake.
Figure S4: Finite-fault slip model of the May 24, 2014 earthquake.
Figure S5: Timeseries of the daily vertical coordinates.
1
Figure S6: Predicted vertical displacements for the geodetic models.
Figure S7: Coulomb stress changes due to the double fault of the 2014 earthquake.
Table S1: Epicenter list of the main events in NAT the last 50 years.
Table S2: Epicenter list of the main aftershocks of the May 24, 2014 earthquake.
Table S3: Displacement GPS vectors of the May 24, 2014 earthquake.
Movie S1: Movie of the finite-fault slip evolution.
2
Text S1.
Details of the methodology of the Waveform Inversion for Source Parameters and for
Finite-Fault Slip Modeling
Waveform Inversion for Source Parameters
In order to compute the strike, dip and rake angles, the focal depth, the seismic moment
and source time functions of the source teleseismic long-period waves were inverted using the
Moment Tensor 5 (MT5) body-waveform algorithm [Nàbělek 1984; McCaffrey et al., 1991;
Zwick et al., 1994]. The epicenter location was assumed fixed to that of USGS-NEIC values. For
long-period P- and SH- waveforms the attenuation parameter t* (t*=t/Q, t: travel time and Q:
average attenuation along the ray path) was selected to be 1.0s and 4.0s, respectively [Futterman,
1962]. The effect of the uncertainties in t* was predominantly assigned on source duration and on
seismic moment, rather than source orientation or focal depth [McCaffrey and Aber’s, 1988;
Taymaz et al., 1990; 1991; 2007a; 2007b; Taymaz and Price, 1992; Tan and Taymaz, 2006;
Yolsal-Çevikbilen and Taymaz, 2012; Fielding et al., 2013; Yolsal-Çevikbilen et al., 2014;
Çubuk et al., 2014].
Velocity responses were deconvolved from the records and then were re-convolved using
the response of the 15–100s long-period instruments of the old World Wide Standard
Seismographic Network (WWSSN). Synthetic waveforms were formed by the combination of
direct (P or SH) and reflected (pP and sP, or sS) phases from a point source embedded in a given
velocity structure. We used a half-space source velocity model, including a water layer with a
depth appropriate to USGS-NEIC epicenter, consisting of P-wave velocity Vp =6.5 km/s, S-wave
velocity Vs =3.7 km/s, and density ρ = 2.9 g/cm3 given by Zwick et al. [1994], Makris and
Stobbe, [1984] and Taymaz et al. [1990; 1991], a simplified crustal model for teleseismic
waveform modeling with the MT5 algorithm. Based on bathymetry data, we defined a water layer
with a velocity of Vp = 1.5 km/s and thicknesses of 750 m [Smith and Sandwell, 1997a; 1997b].
More complex velocity models may appear more tempting, but it is questionable whether they
may lead to better estimates of the centroid depth. Also, that receiver structures and the medium
below them were assumed to correspond to homogeneous half-spaces. The seismograms were
weighted according to the azimuthal distribution of stations, and smaller weights were given to
clusters of stations and larger weights to isolated stations [McCaffrey et al., 1991]. Jeffreys and
Bullen [1940, 1958] travel-time tables were used to calculate the arrival times.
It was found that the estimates of the above inversion were weakly only correlated. Hence,
if one parameter is fixed to an a priori value not differing more than a few degrees or kilometers
from the value offering minimum misfit between observed and synthetic seismograms, the
inversion procedure was leading to estimates of the other parameters also corresponding to
optimal (minimum misfit) solutions. The obvious complexities of P- and of SH- waves are
indicative of strike-slip faulting at shallow focal depth, as well as directivity effect of the rupture
front.
Furthermore, we have done uncertainty test to find the degree of this misfitting between
observed and synthetic waveforms. The inversion returns the minimum misfit solution for the
strike, dip, rake angles and focal depth and seismic moment values between the synthetic and
observed seismograms in a weighted least square’s sense. It is widely reported that [see Taymaz
et al., 1990; 1991; 2004; 2007a; Kiratzi and Louvari, 2001; Tan and Taymaz, 2006; YolsalÇevikbilen et al., 2012, 2014; Fielding et al., 2013] the covariance matrix associated with the
minimum misfit solution usually underestimates the true uncertainties. Hence, we followed the
procedure proposed by McCaffery and Nabelek [1987] and Molnar and Lyon-Caen [1989] to find
more realistic uncertainties.
3
Details of the Finite-Fault Slip Modeling
Finite-fault slip distributions were investigated using an inversion scheme developed by
Yagi and Kikuchi [2000] based on Jeffreys-Bullen [1940, 1958] velocity-depth models.
Teleseismic broad-band P-waveforms are windowed for 60 s, starting 10 s before the origin time.
Velocity seismograms were first band-filtered between 0.01 and 0.8Hz and then were converted
into displacements adopting a sampling interval of 0.25s. The earthquake source model is
constructed using, a standard waveform inversion scheme given by Hartzell and Heaton [1983].
The basic assumption is that the rupture can be approximated by a single fault plane, and
that the slip (rake) angle remained constant during the strong motion. The fault plane was
assumed to consist of a grid of sub-faults, as analyzed in the main text. The source-time (sliprate) function of each sub-fault was expanded in a series of overlapping triangle functions each
with a rise time of 1.25 s. Green's functions are calculated using the method of Kikuchi and
Kanamori [1991]. We also applied smoothing on the slip distribution in space and time in order to
prevent an instability that might occur due to local minima through high number of model
parameters. Further details of finite-fault slip inversion can be found at relevant studies [Hartzell
and Heaton, 1983; Yagi and Kikuchi, 2000; Yagi et al., 2003].
The stress drop (Δσ) was estimated using the equation below based on the assumption of a
circular crack [Aki, 1972; Kanamori, 1994]
 
7 3/2 M 0
16 A3/2
Text S2.
Details of geodetic data and validation of the PPP solutions
As was mentioned in the main text data from 11 permanent GPS stations were analyzed
three weeks before and after the earthquake on 2014.05.24 (data period : from 2014.05.03 to
2014.06.14). Daily 30-s records were obtained for all the stations, except for station IPSA for the
days 2014.05.05, 2014.05.20-21 and 2014.06.06-14 and for station CANA for the days
2014.05.08, 2014.05.18-19, 2014.05.31 and 2014.06.01-02. In addition, the available records of
CANA on 2014.05.07, 2014.05.09, 2014.05.30, 2014.06.03, 2014.06.11 and on 2014.05.13 were
less than 24 hours long.
The GPS data for each station have been processed using the Precise Point Positioning
[PPP; Zumberge et al., 1997; Héroux and Kouba, 2001] method and the GrafNav software ver.
8.40. Elevation-dependent weighted solutions have been obtained using an elevation mask of 7.5o
and final precise orbits (IGb08) and clock data (sp3 and clk files) computed at the CODE IGS
Analysis Centre, providing higher frequency information compared to conventional final IGS
products. The ionosphere-free linear combination was used for the elimination of the ionospheric
influence. The tropospheric zenith delay was modeled as a state in a Kalman filter.
For the validation of the PPP results in the vertical component (see section 3.2 in main text)
part of the data have been processed in an alternative way. The distant 020A station (about 130
km away from the epicentral area; Figure 3) was regarded as a reference station (fixed). The GPS
observations of stations 036A, 022A, 019A, 018B and 089A were then adjusted using the
baseline technique and the Trimble Business Center ver. 1.12 software. The results from this
alternative analysis show that no significant vertical displacements can be documented in any of
the above stations, including near-field stations 089A and 018B. This confirms previous, PPPbased results and indicates that within the limits of accuracy of elevation changes, a few
millimeters, GPS stations captured only horizontal crustal deformation.
4
Figure S1. Location of the (a) near field (0°<Δ<30°) and teleseismic (30°<Δ<90°) stations used
in P- wave first motion polarity distribution (b) teleseismic long-period P- and SH- stations used
in point-source inversion (c) Teleseismic broad-band P- stations used in finite-fault source
inversion.
Figure S2. Distributions of P- wave first motion polarities of the, 2014 earthquake recorded by
regional and teleseismic stations. Black and white circles show up and down P-wave polarities,
respectively. Lower hemisphere equal area projections are used. The station positions have been
plotted with the same velocity model beneath the source used in our minimum misfit solution.
Nodal planes are those of the minimum misfit solution. Station codes and epicentral distances are
given above and below waveforms, respectively. An arrow marks the onset of second-event 13 s
after the first event (see also Figure 2a-b in main text). ANTO station is equipped with Geotech
KS-36000-I Borehole seismometer, and the others are Strekeisen (STS) Very Broad Band (VBB)
seismometers.
5
Figure S3. Comparison of our minimum misfit solution of the 2014 earthquake with the source
parameters reported by USGS-NEIC and Harvard-CMT catalogs. The top row shows selected
waveforms from our preferred long-period minimum misfit solution. The stations are identified at
the top of each column, with the type of waveform marked by P- and SH- and followed by the
instrument type. At the start of each row are the P- and SH- focal spheres for the focal parameters
represented by the five numbers (strike, dip, rake, depth and seismic moment), showing the
positions on the focal spheres of the stations chosen. X and  show matches of observed to
synthetic waveforms that are worse and better than in the minimum misfit solution, respectively.
An arrow marks the onset of second-event 13 s after the first event (see also Figure 2a-b in main
text).
6
Figure S4. Focal mechanism, co-seismic slip distribution, and total moment rate function of the
main earthquake and comparison of the observed (black) and synthetic (red) broadband P
waveforms used in body-wave finite-fault slip-distribution inversion. Station code and maximum
amplitude are shown above the waveforms, station azimuth, and distance below.
7
Figure S5. Variations of daily coordinates for four representative stations in vertical axis for an
interval of 21 days before and after the day of the earthquake (dashed line). 2-σ uncertainty
intervals are shown.
Figure S6. Contour pattern of the modeled vertical displacements for (a) the single fault and (b)
the double fault (see main text, Section 3.3). The location of GPS stations is marked by triangles
with the station code. Results were produced using the Coulomb 3.3 software.
8
Figure S7. Coulomb stress changes due to the double fault of the 2014 earthquake. The scale of
the changes is indicated by the color bar to the right (in bars) The calculations were made at a
depth of 10km (approximate middle of the geometric fault model, compatible to focal depth), for
the average values of strike, dip and rake, 72o, 90o and 179o, respectively. Aftershocks are marked
by gray circles. Results produced using the Coulomb 3.3 software.
9
Table S1. Source parameters of North Aegean Trough earthquakes (see Figure 3). List reported
by TT91: Taymaz et al. [1991] and TY15: Taymaz and Yolsal-Çevikbilen [2015]. Lat: Latitute
(°N), Lon: Longitude (°E), : strike angle, : dip angle, : rake angle, Mo: Seismic Moment
(Newton – meter), h: focal depth (km). For earthquake magnitude, w and s represent moment and
surface wave magnitudes, respectively. Epicenter locations are taken from ISC earthquake
catalogue except for 2013-2014 earthquakes (USGS-NEIC).
Origin
time (to)
(h: m :s)
09.03.1965 17:57:54
27.03.1975 05:15:07
Date
(d. m. y)
Ms
Mw
Lat.
(°N)
Lon.
(°E)
39.34
40.45
23.82
26.12
6.3
6.6
18.01.1982 19:27:25
39.96
24.39
6.9
06.08.1983
06.07.2003
24.05.2014
Source-2
40.14
40.45
40.29
40.44
24.74
26.04
25.45
25.87
6.9
5.7
6.7
6.5
15:43:51
19:10:27
09:25:03
09:25:16
*
Strike
(, °)
Dip
(, °)
135±5
68±8
85±5
55±8
Rake
(, °)
h
(km)
Mo
(101
6 Nm)
147
200
15+3/-7
7±2
-145±8
15±3
187233±5
62±5
7±1
732
10/+7
47-5/+8 83±6 180±10
7±1
1940
168
86
10
8
40.6
75±5
85±5 -178±5
11±2 1550
242
80
-176
11
677
Slip
vector
(°)
045
046
Ref.
TT91
TT91
050
TT91
047
078
075
061
TT91
TY15
This
study
Table S2. Important (Mw>4.0) events of the 2014 seismic sequence. Aftershocks correspond to
rather distinct clusters (see Figure 1 for location and epicenter distribution). Data retrieved from
ECP14: Evangelidis [2014] (relocated) and National Observatory of Athens (NOA) database
(preliminary).
a/a
Date-UTC time
Longitude (o)
Latitude (o)
Depth (km)
Magnitude
Ref
1
24/5/2014-09:25
25.3982
40.2970
15.86
6.8 Mw
ECP14
2
24/5/2014-09:31
26.1335
40.4675
18.98
4.9 ML
ECP14
3
24/5/2014-09:34
24.3791
40.0510
22.11
4.6 ML
ECP14
4
22/8/2014-04:27
23.4610
39.9228
28.7
5.1 Mw
NOA
5
04/9/2014-17:43
24.9012
40.1515
15.08
4.9 Mw
ECP14
10
Table S3. GPS-derived displacements used in the analysis. For location see Figure 1 in main text.
Longitude
Latitude
dE
dN
σE
σN
(o)
(o)
(mm)
(mm)
(mm)
(mm)
018B
25.524
40.474
96.9
32.0
0.7
1.0
089A
25.201
39.908
-23.0
-52.0
0.6
0.8
019A
25.745
40.855
14.3
13.1
0.6
0.8
036A
24.612
40.777
9.4
-5.4
0.7
0.8
076A
23.944
40.039
3.0
-1.7
0.7
0.8
020A
26.389
41.270
6.7
5.9
0.6
0.8
022A
26.022
41.233
5.5
8.6
0.6
0.8
069A
25.289
41.090
8.5
3.4
0.4
0.6
091A
26.106
39.249
-0.7
-4.0
0.6
0.8
CANA
26.414
40.111
-27.0
14.0
0.7
0.9
IPSA
26.380
40.918
12.7
15.4
0.7
0.8
Site
Movie S1. WMV movie of the finite-fault slip evolution for the model shown in Figure 3 of the
main text is represented as an animation of the cumulative slip distribution for various times (1s –
40s) after rupture initiation at the hypocenter (white star). The animation is approximately in real
time. The color scale shows the amount of slip in meters.
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14