Designing the configurationof the

Geodetic-Geodynamic Network in Israel

Gilad Even-TzurDepartment of Mapping and Geo-Information Engineering

Faculty of Civil and Environmental EngineeringTECHNION - Israel Institute of Technology

ISGDM-2005, 17-18 March, Jaén , Spain

The Geodetic-Geodynamic Network (G1)

► Includes 160 points that homogeneously cover the state of Israel (Blue circles and Red squares)

► The location of the points was determined mainly according to geological considerations

►The points were built according to very high technical specifications, to ensure their geotechnical stability

The goal of the Geodetic-Geodynamic Network

► A potential geodetic network for monitoring deformations in primary and secondary known faults

► Serves as the major geodetic control network of Israel

The First Measurement Campaign

► During 1996 the G1 network was measured for the first time

► The network was measured by four GPS receivers

► Sessions of 24 hours

► Most network points were measured in two independent sessions

►The data processing was carried out using the BERNESE

The Network Sensitivity

► Based on the first campaign, a sensitivity analysis was performed in the northern part of the network

► The analysis indicated that the sensitivity of the network was too low

► The analysis also indicated that an identical second measurement campaign will not be sufficient to detect possible movements and deformations

A new network design is needed

Network Configuration of the Second Campaign

► The second campaign was held in 2002

► Only 100 points were measured (Blue circles)

► 5 new points were fixed in the northern part of the network (Yellow circles )

► 11 continuous permanent GPS stations were operated (Green triangles)

Vector Configuration Design of the Network

► An effective design of the GPS measurements decreases campaign costs and increases the accuracy and reliability of the network

► The goal of the design is to improve the network, so that it would enable the detection and measurements of expected movements and deformations

► A method, based on sensitivity analysis, was used for the GPS vector configuration design

► The method uses a velocity field of the network points, calculated from an assumed geological model

Geological Model

Dy

tanπV

v 1x

mm/yr5V

km10D

► Locked Fault model in the Dead Sea Rift

the fault is locked from the surface down to depth D, and slips freely below this depth by V millimeters per year

-2.5-2

-1.5-1

-0.50

0.51

1.52

2.5

-60-40-200204060

y (km)

velo

city

( mm

)

Sensitivity Analysis► Based on statistical test of Hypothesis

dr20

xT

Fr

xQxt ,

ˆ ~ˆ

ˆˆ

0x:H

0x:H

1

0

ˆ

ˆ

Accepted if:

Accepted if:

,,

,,

dr

dr

Ft

Ft

20

xT xQx

►If is true, the test statistic has a non-central F distribution with non-centrality parameter given by:

1H

Sensitivity Analysis

► We define as the boundary value of λ, which will cause the null hypothesis to be rejected at probability levels α and β, the value is an implicit function

►Our aim is designing a monitoring network, which will enable the rejection of the null hypothesis and the acceptance of the alternative hypothesis Sensitive Network

0λ

0λ

Sensitivity Analysis

►Since the first GPS campaign has already been carried out in 1996 N1 has been defined

►We create the normal matrix N2 which contains the sessions with the most effective contribution to the sensitivity of the network

2T

Tx0 1 1 1 2 12 2

0 0

tx Q x

x N N N N N x

8 sessionsprovide a sufficiently sensitive network

Configuration Design of the Network

►To increase the reliability of the network, each point was measured in three independent sessions

►The duration of each session was planned for 8 hours with epoch interval of 30 sec

►The network was designed for measurements using four receivers

92 sessions for 105 points

Broken lines - The eight sessions that provide sufficiently sensitive network

The designed sessions of the northern part of the Geodetic-Geodynamic network

The ability of the networkto sense horizontal velocity

The typical precision of the network points:

►1996 :3-4 mm for the horizontal component

►2002 :2-3 mm for the horizontal component

We can roughly estimate the ability of the network to sense horizontal velocity along the Dead Sea rift for a

velocity of two millimeters per year