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Journal ArticleDOI

GPS evidence for northward motion of the Sinai Block: Implications for E. Mediterranean tectonics

30 Sep 2005-Earth and Planetary Science Letters (Elsevier)-Vol. 238, Iss: 238, pp 217-224

Abstract: GPS survey sites in the Sinai Peninsula show northerly motion relative to Africa (Nubia) at 1.4F0.8 mm/yr north and 0.4F0.8 mm/yr west. Continuous IGS GPS sites in Israel, west of the Dead Sea fault show a similar northerly sense of motion relative to Nubia (2.4F0.6 mm/yr north and 0.04F0.7 mm/yr east), suggesting that the entire Sinai Block south of Lebanon is characterized by northward translation relative to the Nubian plate. We develop an elastic block model constrained by the GPS results that is consistent with the regional tectonics and allows us to estimate slip rates for Sinai bounding faults, including the Gulf of Aqaba–southern Dead Sea fault system (~4.4F0.3 mm/yr, left lateral), the Gulf of Suez (1.9F0.3 mm/yr left lateral, and 1.5F0.4 mm/yr extension), and the Cyprus Arc (predominantly convergence at 8.9F0.4 mm/yr along the western segment, and ~6.0F0.4 mm/yr left lateral, strike slip along the eastern segment). These observations imply that the Sinai Peninsula and Levant region comprise a separate sub-plate sandwiched between the Arabian and Nubian plates. D 2005 Elsevier B.V. All rights reserved.
Topics: Strike-slip tectonics (51%)

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GPS evidence for northward motion of the Sinai Block:
Implications for E. Mediterranean tectonics
Salah Mahmoud
a,
*
, Robert Reilinger
b,2
, Simon McClusky
b,2
,
Philippe Vernant
b,2
, Ali Tealeb
a,1
a
National Research Institute for Astronomy and Geophysics, Helwan, Cairo, Egypt
b
Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, MA, USA
Received 18 November 2004; received in revised form 8 June 2005; accepted 10 June 2005
Available online 22 August 2005
Editor: S. King
Abstract
GPS survey sites in the Sinai Peninsula show northerly motion relative to Africa (Nubia) at 1.4 F 0.8 mm/yr north and
0.4 F0.8 mm/yr west. Continuous IGS GPS sites in Israel, west of the Dead Sea fault show a similar northerly sense of motion
relative to Nubia (2.4 F0.6 mm/yr north and 0.04F0.7 mm/yr east), suggesting that the entire Sinai Block south of Lebanon is
characterized by northward translation relative to the Nubian plate. We develop an elastic block model constrained by the GPS
results that is consistent with the regional tectonics and allows us to estimate slip rates for Sinai bounding faults, including the
Gulf of Aqaba–southern Dead Sea fault system (~4.4 F0.3 mm/yr, left lateral), the Gulf of Suez (1.9 F 0.3 mm/yr left lateral,
and 1.5F0.4 mm/yr extension), and the Cyprus Arc (predominantly convergence at 8.9 F 0.4 mm/yr along the western
segment, and ~6.0 F0.4 mm/yr left lateral, strike slip along the eastern segment). These observations imply that the Sinai
Peninsula and Levant region comprise a separate sub-plate sandwiched between the Arabian and Nubian plates.
D 2005 Elsevier B.V. All rights reserved.
Keywords: global positioning system; neotectonics; Sinai; plate tectonics; east Mediterranean
1. Introduction
The Sinai Peninsula (Fig. 1) lies at the northern end
of the Red Sea. Early plate tectonic models [1] iden-
tified the southern-most Sinai as lying near a rift–rift-
transform triple junction (Red Sea, Gulf of Suez, Gulf
of Aqaba/Dead Sea fault). Early seismotectonic stu-
dies of the Sinai area [2] considered the Sinai to be
part of the African plate that is bsplinteringQ off the
main African plate as a result of the collision with
0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.epsl.2005.06.063
* Corresponding author. Tel.: +20 2 5560 046; fax: +20 2 554 80
20.
E-mail addresses: salahm55@yahoo.com (S. Mahmoud),
reilinge@erl.mit.edu (R. Reilinger).
1
Tel.: +20 2 5560 046; fax: +20 2 554 80 20.
2
Tel.: +1 617 253 7860; fax: +1 617 253 6385.
Earth and Planetary Science Letters 238 (2005) 217 224
www.elsevier.com/locate/epsl

Eurasia. Recently, Salamon et al. [3] defined the Sinai
tectonic block as a separate entity from Africa with
the main Africa–Sinai boundary being extensional and
lying within the Gulf of Suez. The Gulf of Aqaba–
Dead Sea fault (DSF) system forms the eastern bound-
ary with Arabia. The northern and northwestern (i.e.,
north of the Gulf of Suez) boundaries of the Sinai
Block are not well defined [4], but the northern
boundary may correspond to the active collision/sub-
duction boundary along the Cyprus Arc (Fig. 1).
The tectonic history of the Sinai region is inti-
mately tied to the separation of the Arabian plate
from Africa (Nubia) along the Red Sea rift system.
Opening of the Red Sea was initiated in the early
Oligocene [5,6]. The Red Sea rift basin was well
established by early Miocene at which time rifting
was concentrated along the Red Sea and its northern
extension along the Gulf of Suez [7]. The Sinai
Peninsula was formed in Middle to Late Miocene
with the formation of the Gulf of Aqaba–DSF system.
Fig. 1. Topographic (SRTM30) and tectonic map of the Sinai and surrounding region. Dots show seismicity (NEIC), focal mechanisms are from
Harvard CMT. Inset shows location of study area within the context of the eastern Mediterranean. DSF=Dead Sea fault, Gulf of Iske.=Gulf of
Iskenderum.
S. Mahmoud et al. / Earth and Planetary Science Letters 238 (2005) 217–224218

At this time, spreading in the Gulf of Suez slowed and
the Red Sea–Gulf of Aqaba/DSF became the principal
Nubian–Arabian boundary [8].
The southern and central Red Sea is characterized
by active ocean spreading with rates varying from ~15
mm/yr in the south to ~6 mm/yr in the northern rift
[9,10]. At present, the rate of extension across the
Gulf of Suez is thought to vary from zero in the north
to ~1 mm/yr in the south [11]. The Gulf of Aqaba–
DSF system is predominantly left-lateral strike slip
with a small component of extension in the south
(Gulf of Aqaba) and increasing compression towards
the north. Estimates of current fault slip rates in the
Gulf of Aqaba and along the DSF vary considerably
(e.g., see [12] for references). Recent GPS observa-
tions in Israel (confined primarily to the west side of
Fig. 2. Simplified tectonic map of the Sinai and surrounding regions showing GPS velocities and 95% confidence ellipses relative to Nubia.
Lines with tick-marks are normal faults, ticks on downthrown block, double line is Red Sea rift, plain lines are strike-slip faults. GPS velocities
are given in Table 1.
S. Mahmoud et al. / Earth and Planetary Science Letters 238 (2005) 217–224 219

the Dead Sea fault) have been interpreted to indicate
left-lateral slip at 3.7 F 0.4 mm/yr [12], while neotec-
tonic studies suggest left-lateral slip at 4 F 2 mm/yr
since the Late Pleistocene [13]. These rates are lower
than, but not significantly different (at 95% confi-
dence) from GPS estimates based on Arabia–Nubia
overall motion, 5.8 F 1 mm/yr that ignore possible
Sinai Block motion ([10]; 95% confidence errors are
about 2.5
1-sigma uncertainty ). As noted by
McClusky et al. [10], northward motion of the Sinai
would reduce geodetic estimates of slip rate on the
DSF.
Because of its position within the zone of interac-
tion of the African (Nubian), Arabian, and Eurasian
(more properly, Anatolian) plates (Fig. 1), the tec-
tonics of the Sinai region play a pivotal role in eastern
Mediterranean kinematics. In addition, quantifying
Sinai Block motion is necessary to constrain slip
rates on the principal faults in the region, and conse-
quently for evaluating earthquake hazards, particu-
larly in the greater Cairo area and along the DSF.
In this paper we present GPS-derived velocities for
a network of survey sites on the Sinai Peninsula and
along the west side of the Gulf of Suez. We use these
velocities, and the velocities of IGS-GPS stations in
Israel [12] to constrain an elastic block model to test
the consistency of the GPS velocities with coherent
block motion and to estimate slip rates on block-
bounding faults.
2. GPS velocity field
Fig. 2 shows GPS-derived velocities in the Sinai
network along with velocities from continuously
recording stations in surrounding areas relative to
Nubia. Table 1 lists the velocity estimates and stan-
dard deviations. With the exception of sites CATH
and KENS that were measured 4 times between 1997
and 2000 (sites destroyed), velocities for Sinai survey
sites were determined from 5 to 7 surveys conducted
between 1996 and 2003.
We analyze the GPS data using the GA MIT/
GLOBK software [14,15] in a two-step approach
[16]. In the first step, we use GPS phase observations
from each day to estimate station coordinates, the
zenith delay of the atmosphere at each station, and
orbital and Earth orientation parameters (EOP). In the
second step we use the loosely constrained estimates of
station coordinates, orbits, and EOP and their covar-
iances from eac h day, aggrega ted by survey, as quasi-
observations in a Kalman filter to estimate a consistent
set of coordinates and velocities. We provide orbital
control and tie the regional Sinai meas urements to an
external global reference frame by including in the
regional analysis data from 3–5 continuously operat-
ing IGS stations for each da y. The regional quasi -
observations are then combined with quasi-observa-
tions from an analysis of phase data from over 100
stations performed by the Scripps Orbital and Perma-
nent Array Center (SOPAC) at UC San Diego [17].
Before estimating velocities in the second step of our
analysis, we examine the tim e serie s of position esti-
Table 1
GPS velocities in an Africa (Nubia)-fixed reference frame and
1-sigma uncertainties for sites shown in Fig. 2
Site Long. Lat. VE VN EF NF
(8E) (8N) (mm/yr)
UDMC 36.285 33.510 0.1 (0.8) 6.2 ( 0.3) 1.0 1.0
SENK 36.131 36.050 2.7 (1.0) 4.5 (0.5) 0.7 0.6
HALY 36.100 29.139 3.8 (1.4) 6.8 (0.2) 0.9 0.9
ELRO 35.771 33.182 0.3 (0.2) 5.6 (0.4) 0.7 0.7
KATZ 35.688 32.995 0.7 (1.0) 6.3 (1.5) 0.5 0.5
GILB 35.416 32.479 1.3 ( 0.9) 4.0 (0.8) 0.6 0.6
DRAG 35.392 31.593 0.0 ( 0.1) 3.2 ( 0.2) 0.7 0.7
JSLM 35.302 31.771 0.5 ( 0.4) 2.9 (0.2) 1.0 1.0
KABR 35.145 33.023 1.4 ( 0.9) 2.5 (0.0) 0.6 0.6
BARG 35.089 31.723 0.7 (1.0) 1.6 ( 1.1) 1.2 1.2
BSHM 35.023 32.779 1.2 ( 0.7) 2.9 (0.5) 0.5 0.5
ELAT 34.921 29.509 1.8 (0.8) 3.2 ( 0.3) 0.6 0.6
LHAV 34.866 31.378 0.6 ( 0.5) 2.0 ( 0.4) 0.8 0.8
TELA 34.781 32.068 0.6 (0.9) 1.8 ( 0.5) 0.5 0.5
RAMO 34.763 30.598 2.8 (2.8) 3.0 (0.5) 0.6 0.6
DAHA 34.470 28.529 0.8 ( 2.4) 1.8 ( 1.3) 0.7 0.7
NABQ 34.314 28.178 0.1 ( 0.7) 2.4 (0.2) 0.9 0.8
SHAM 34.184 27.846 1.2 ( 1.9) 1.6 ( 0.3) 0.6 0.6
CATH 33.995 28.639 1.4 (1.1) 0.8 ( 1.3) 1.3 1.3
KENS 33.883 27.961 2.3 ( 2.7) 3.1 (1.7) 1.0 1.0
HURG 33.832 27.244 1.1 ( 1.8) 0.2 ( 0.0) 0.9 0.8
TOUR 33.596 28.269 0.9 ( 1.1) 0.7 ( 0.6) 0.6 0.6
GEMS 33.494 27.686 0.6 (0.1) 0.5 ( 0.7) 0.7 0.7
DERB 33.404 28.631 0.6 ( 0.7) 0.6 ( 2.1) 0.7 0.7
NICO 33.396 35.141 3.7 (1.5) 2.5 (0.4) 0.6 0.6
ZEIT 33.391 27.919 0.3 ( 0.1) 1.7 (1.3) 0.7 0.7
GARB 33.228 28.163 0.3 ( 0.2) 1.6 (1.1) 0.7 0.7
ABOZ 33.102 29.141 1.2 (1.2) 1.2 ( 0.4) 0.7 0.7
FANA 32.566 29.379 0.9 (0.7) 1.4 (1.0) 0.6 0.6
HELW 31.344 29.862 0.2 (0.1) 0.1 (0.3) 0.6 0.6
Numbers in brackets are residual velocities from the block model
shown in Fig. 3.
S. Mahmoud et al. / Earth and Planetary Science Letters 238 (2005) 217–224220

mates to determine the appropriate weights to be
applied to each group’s surveys. For the velocity solu-
tion, we re-weight the quasi-observations such that the
normalized long-term scatter in horizontal position for
each group is equal to one. Finally, to account for
correlated errors, we add to the assumed error in
horizontal position a random walk compo nent of 2
mm/Myr [18]. Uncertainties quoted in the text and
tables are 1-sigma estimates while those shown in
the figures are 95% confidence ellipses.
3. Motion of the Sinai Block
The GPS-velocity estimates shown in Fig. 2 and
listed in Table 1 are given in a Nubia-fixed reference
frame determined in this study by minimizin g the
velocities of GPS stations on the Nubian plate [10].
While velocity estimates for Sinai stations relative to
their uncertainties are small, they indicate a generally
consistent sense of motion towards the north at an
average rate of 1.4 F 0.8 mm/yr, with a possible wes-
terly component of 0.4 F 0.8 mm/yr. This same sense
of motion, perhaps at a higher rate, characterizes IGS
sites further north in Israel (Fig. 2, Table 1) as was
also noted by Wdowinski et al. [12]. The average
north rate for the five Israel IGS stations more than
45 km west of the main trace of the DSF (KABR,
BSHM, TELA, LHAV, RAMO; see Fig. 2 and Table
1) is 2.4 F 0.6 mm/yr, with an insignificant westerly
component of 0.04 F 0.6 mm/yr. This northerly rate is
nominally higher, but not significantly different from
the new GPS results in the southern Sinai Peninsula.
The consistent GPS evidence for northward motion of
the southern Sinai Peninsula from survey-mode GPS
and the continuous IGS stations in Israel suggests that
the Sinai Peninsula and the Levant west of the DSF in
Israel move roughly coherently relative to Nubia. The
variability of the Sinai survey results may reflect local
disturbances associated with benchmark inst ability,
hydrologic effects, local fault motions, or statistical
fluctuations due to survey noise. The tendency for
GPS sites on the west side of the Gulf of Suez to
move roughly coherently with those on adjacent parts
of the Peninsula indicates that present-day deforma-
tion associated with the western Sinai boundary
includes the easternmost section of the Nubian crust
west of the Gulf proper. This is consi stent with the
occurrence of large faults associated with the Gulf
opening extending well west of the present boundaries
of the Gulf itself [11], and with the distributed nature
of seismic activity along the Gulf [3] (Fig. 1).
To test further the hypoth esis of coherent motion of
the Sinai Block, and to investigate the implications of
the GPS data for slip rates on major faults, we have
developed a block model following the procedure
described by Meade et al. [19]. Prescribed parameters
for the model include fault locations, and fault locking
depths. The GPS data are used to constrain relative
block motions. The model includes the effects of
elastic strain accumulation on block bounding faults.
Block motions are computed by minimizing in a least
squares sense the residual GPS velocities (i.e.,
observed–modeled). For the model used here, all faults
are vertical except for the western segment of the
Cyprus Arc that has a 308 dip to the NE. Fig. 3
shows our prefer red model with the Sinai Block
bounded by the Gulf of Aqaba/DSF system on the
east, the Gulf of Suez on the west, and the Cyprus
Arc to the north. North of the Gulf of Suez there is little
evidence for active faulting [4], so the western Sinai
boundary in Fig. 3 is not well established. For this
model, we use a 13 km locking depth for the DSF
(constrained by the model by minimizing the weighted
root mean square [wrms] residual velocities, see inset,
Fig. 3) and 15 km for other faults (unconstrained). Fig.
3 shows residual velocities in and around the Sinai
Block for this model (listed in Table 1). Euler vectors
for Sinai, Nubia, and Arabia relative to Eurasia result-
ing from this model are given in Table 2. The Nubia
and Arabia Euler Vectors are in good agreement with
those reported by McClusky et al. [10].
Fault slip rates on Sinai block-bounding faults are
given in Fig. 3. These slip rates depend on the angle
between the direction of relative motion between
adjacent blocks and the local strike of the fault defin-
ing the block boundary at that location. The fault-
normal rate varies as the sine of this angle and the
fault parallel rate as the cosine. This is well illustrated
by the variation in slip rates along the Dead Sea Fault
at the Lebanon restraining bend (Fig. 3). Since the
regional strikes of the better-defined faults are well
constrained, the slip rates we report should be appro-
priate regional averages. On the other hand, local
variations in fault strike will result in variations in
fault-parallel and fault-normal slip rates that need to
S. Mahmoud et al. / Earth and Planetary Science Letters 238 (2005) 217–224 221

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Abstract: We present and interpret Global Positioning System (GPS) measurements of crustal motions for the period 1988–1997 at 189 sites extending east-west from the Caucasus mountains to the Adriatic Sea and north-south from the southern edge of the Eurasian plate to the northern edge of the African plate. Sites on the northern Arabian platform move 18±2 mm/yr at N25°±5°W relative to Eurasia, less than the NUVEL-1A circuit closure rate (25±1 mm/yr at N21°±7°W). Preliminary motion estimates (1994–1997) for stations located in Egypt on the northeastern part of Africa show northward motion at 5–6±2 mm/yr, also slower than NUVEL-IA estimates (10±1 mm/yr at N2°±4°E). Eastern Turkey is characterized by distributed deformation, while central Turkey is characterized by coherent plate motion (internal deformation of <2 mm/yr) involving westward displacement and counterclockwise rotation of the Anatolian plate. The Anatolian plate is de-coupled from Eurasia along the right-lateral, strike-slip North Anatolian fault (NAF). We derive a best fitting Euler vector for Anatolia-Eurasia motion of 30.7°± 0.8°N, 32.6°± 0.4°E, 1.2°±0.1°/Myr. The Euler vector gives an upper bound for NAF slip rate of 24±1 mm/yr. We determine a preliminary GPS Arabia-Anatolia Euler vector of 32.9°±1.2°N, 40.3°±1.1°E, 0.8°±0.2°/Myr and an upper bound on left-lateral slip on the East Anatolian fault (EAF) of 9±1 mm/yr. The central and southern Aegean is characterized by coherent motion (internal deformation of <2 mm/yr) toward the SW at 30±1 mm/yr relative to Eurasia. Stations in the SE Aegean deviate significantly from the overall motion of the southern Aegean, showing increasing velocities toward the trench and reaching 10±1 mm/yr relative to the southern Aegean as a whole.

1,773 citations


Journal ArticleDOI
J. Dercourt1, L.P. Zonenshain, L. E. Ricou1, V. G. Kazmin  +15 moreInstitutions (2)
15 Mar 1986-Tectonophysics
Abstract: We discuss nine palinspastic geological maps (Plates 1–9), at 1 20,000,000 scale, which depict the evolution of the Tethys belt from the Pliensbachian (190 Ma) to the Tortonian (10 Ma). A Present structural map (Plate 10) is shown for comparison at the same scale with the same conventions. Our reconstructions are based on a kinematic synthesis (Savostin et al., 1986), a paleomagnetic synthesis (Westphal et al., 1986) and geological compilations and analyses concerning in particular the western domain (Ricou et al., 1986), the eastern passive margins (Kazmin et al., 1986a), the eastern active margins (Kazmin et al., 1986b), the Black Sea-Caspian Sea basins (Zonenshain and Le Pichon, 1986) and the ophiolites (Knipper et al., 1986).

1,491 citations


Journal ArticleDOI
Dan McKenzie1Institutions (1)
18 Apr 1970-Nature
TL;DR: The seismicity and fault plane solutions in the Mediterranean area show that two small rapidly moving plates exist in the Eastern Mediterranean, and such plates may be a common feature of contracting ocean basins.
Abstract: The seismicity and fault plane solutions in the Mediterranean area show that two small rapidly moving plates exist in the Eastern Mediterranean, and such plates may be a common feature of contracting ocean basins. The results show that the concepts of plate tectonics apply to instantaneous motions across continental plate boundaries.

646 citations


Journal ArticleDOI
Simon McClusky1, R. E. Reilinger1, Salah Mahmoud, D. Ben Sari2  +1 moreInstitutions (2)
Abstract: SUMMARY We use continuously recording GPS (CGPS) and survey-mode GPS (SGPS) observations to determine Euler vectors for relative motion of the African (Nubian), Arabian and Eurasian plates. We present a well-constrained Eurasia‐Nubia Euler vector derived from 23 IGS sites in Europe and four CGPS and three SGPS sites on the Nubian Plate (−0.95 ± 4.8 ◦ N, −21.8 ± 4.3 ◦ E, 0.06 ± 0.005 ◦ Myr −1 ). We see no significant (> 1m m yr −1 ) internal deformation of the Nubian Plate. The GPS Nubian‐Eurasian Euler vector differs significantly from NUVEL-1A (21.0 ± 4.2 ◦ N, −20.6 ± 0.6 ◦ E, 0.12 ± 0.015 ◦ Myr −1 ), implying more westward motion of Africa relative to Eurasia and slower convergence in the eastern Mediterranean. The Arabia‐ Eurasia and Arabia‐Nubia GPS Euler vectors are less well determined, based on only one CGPS and three SGPS sites on the Arabian Plate. The preliminary Arabia‐Eurasia and Arabia‐ Nubia Euler vectors are 27.4 ± 1.0 ◦ N, 18.4 ± 2.5 ◦ E, 0.40 ± 0.04 ◦ Myr −1 , and 30.5 ± 1.0 ◦ N, 25.7 ± 2.3 ◦ E, 0.37 ± 0.04 ◦ Myr −1 , respectively. The GPS Arabia‐Nubia Euler vector differs significantly from NUVEL-1A (24.1 ± 1.7 ◦ N, 24.0 ± 3.5 ◦ E, 0.40 ± 0.05 ◦ Myr −1 ), but is statistically consistent at the 95 per cent confidence level with the revised Euler vector reported by Chu & Gordon based on a re-evaluation of magnetic anomalies in the Red Sea (31.5 ± 1.2 ◦ N, 23.0 ± 2.7 ◦ E, 0.40 ± 0.05 ◦ Myr −1 ). The motion implied in the Gulf of Aqaba and on the Dead Sea fault (DSF) by the new GPS Nubia‐Arabia Euler vector (i.e. ignoring possible Sinai block motion and possible internal plate deformation) grades from pure left lateral strike-slip in the Gulf and on the southern DSF with increasing compression on the central and northern DSF with relative motion increasing from 5.6 to 7.5 mm yr −1 (± 1m m yr −1 ) from south to north. Along the northern DSF (i.e. north of the Lebanon restraining bend) motion is partitioned between 6 ± 1m m yr −1 left-lateral motion parallel to the fault trace and 4 ± 1m m yr −1 faultnormal compression. Relative motions on other plate boundaries (including the Anatolian and Aegean microplates) derived from the GPS Euler vectors agree qualitatively with the sense of motion indicated by focal mechanisms for large crustal earthquakes (M > 6). Where data are available on fault-slip rates on plate bounding faults (North Anatolian fault, East Anatolian fault, Dead Sea fault, Red Sea rift), they are generally lower than, but not significantly different from, the full plate motion estimates suggesting that the majority of relative plate motion is accommodated on these structures.

642 citations


Journal ArticleDOI
D. Dong1, Thomas A. Herring2, Robert W. King2Institutions (2)
16 Apr 1998-Journal of Geodesy
Abstract: We discuss an approach for efficiently combining different types of geodetic data to estimate time-dependent motions of stations in a region of active deformation. The primary observations are analyzed separately to produce loosely constrained estimates of station positions and coordinate system parameters which are then combined with appropriate constraints to estimate velocities and coseismic displacements. We define noninteger degrees of freedom to handle the case of finite constraints and stochastic perturbation of parameters and develop statistical tests for determining compatibility between different data sets. With these developments, we show an example of combining space and terrestrial geodetic data to obtain the deformation field in southern California.

367 citations