Printer Friendly

Monitoring active structures in eastern Corinth Gulf (Greece): the Kaparelli fault.

1. INTRODUCTION

The Gulf of Corinth in central Greece is one of the most tectonically active and rapidly extending regions in the world. Surface topography and geomorphology are clearly associated with seismic activity along large normal faults (Armijo et al., 1996). Extension is mainly directed N-S (Clarke et al. 1998). The southern side of the Gulf of Corinth is bound by a series of major north-dipping normal faults, forming a complex asymmetric half graben (Jackson et al., 1982). There are E-W striking normal faults with antithetic dip, i.e. to the south; however, they are visible at the northern edge of the Gulf.

In February-March 1981 a sequence of three earthquakes with magnitudes greater than 6.3 struck the eastern Gulf of Corinth (Hubert et al., 1996). North-dipping surface breaks were noted the morning after the first two events on the southern side of the Gulf (Perachora Peninsula) and south-dipping ruptures appeared on the northern side of the Gulf (Kaparelli region) as a result of the third event (Figure 1; data from Jackson et al., 1982). In both areas seismic motion occurred along basin-bounding faults bringing in contact Mesozoic limestone and alluvial deposits as well as colluvium.

Focal mechanisms of small and shallow earthquakes (data from Ambraseys and Jackson, 1990) also show normal faulting with the active fault plane dipping at about 45[degrees] for faults at the eastern end of the Gulf of Corinth including Kaparelli. Recently, three trenches have been excavated across the Kaparelli Fault (Pavlides et al., 2003; Kokkalas et al., in press). Their stratigraphic record shows at least three events during the Holocene period, with the 1981 event included. The estimated mean slip rate is 0.28 mm/yr. Colluvial tectonostratigraphy and analysis of displacements on key horizons suggests surface rupturing events in the order of 0.7-1 m.

The Kaparelli Fault consists of three segments, two of which were ruptured in 1981 (Jackson et al., 1982). The two-ruptured segments form left-stepping en echelon geometry, while the third north-western segment of the fault did not rupture (Figure 2). The fault segments are clearly expressed at the surface by nearly continuous scarps. The footwall elevation is 600 m and lithology is composed of hard, Mesozoic limestone. The hanging wall block forms a small basin and contains approximately 200 m of fluvial-terrestrial deposits of Pleistocene age as well as Holocene alluvium.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

2. MONITORING THE ACTIVITY OF THE KAPARELLI FAULT

In order to measure the kinematics of deformation in 3-D the Greek group together with the Polish and Slovak groups, have established a dense GPS network and two (2) extensometers. The details of installation of instruments and project rationale are given in Drakatos et al. (2005) and Cacon et al. (2005). In summary, the Slovakian and Greek groups have begun monitoring the Kaparelli fault area since May 2003. On May 26, 2003 they installed an extensometer of TM-71 type (Kostak and Cruden, 1990). A second instrument was installed on July 15, 2004. In addition, a dense GPS network has been installed within a collaboration of Greek and Polish groups, comprising six (6) stations. The network was deployed on November, 11-12 2003 and its first measurement took place in May 2004. The network was expanded on March 31, 2005. Five (5) new stations were installed inside the Asopos rift valley (see Figure 4 below). Both sub-networks were measured during May 2005 and May 2006.

3. MONITORING FAULT MOTION USING TM-71 INSTRUMENTS

The 2003 installation of observation point Kapa1 was done at the trench Kap2 that was excavated across the fault (Figure 2; Pavlides et al., 2003). The TM-71 is fixed to the fault (north side) and to a construction built on the hanging wall (south side) by steel bars. The 2004 installation of Kapa2 was done against a free surface of the fault plane, about 2 km to the west of locality Kap2. The position of the X, Y, and Z axes of the instrument corresponds respectively to: (X) the direction perpendicular to the fault or fault-normal motion, (Y) direction parallel to fault strike or the strike slip motion along the fault surface and (Z) vertical direction or the dip slip component of motion. The instrument readings are recorded on a nearly monthly basis by NOA. Our observations for the site Kapa1 span a period of 3 years so it is possible to make a preliminary interpretation (Figure 3). From November 2003 the course in Kapa1 X-axis shows variations [+ or -]0.25 mm which can be attributed to seasonal temperature variations upon rock and is normal with this type of measurement (Drakatos et al., 2005). An extreme was observed between May and August 2003, (+0.5 mm) followed by a back-movement of -0.85 mm. This occurred in the initial period of measurement when a concrete block settlement after its creation inside the trench may be present. Since 2004 we observe continuous opening that is in agreement with fault kinematics. Displacement along Z-axis is relatively stable. Along the axis Y (horizontal; along the fault strike) observed motion is dextral oblique slip of -0.6 mm between June and November 2004 followed by relative stability. It is interesting to see that a similar pattern was observed in the rotation plots (Figure 3c) for the planes XY (the horizontal plane) and XZ (the vertical plane). Records show change at the same time in the second half of 2004, after which stability re-established. This dextral shear motion is consistent with the slip vector model of Roberts and Ganas (2000) that predict oblique slip vectors at normal fault tips. At Kapa2 the observation period is only two years (X-axis; Figure 3b) and the record needs more time to be interpreted.

[FIGURE 4 OMITTED]

4. MONITORING REGIONAL DEFORMATION USING GPS INSTRUMENTS

The motion of crustal blocks in central Greece can be described in a first approximation by a combination of translation and rotation (Goldsworthy et al., 2002). By combining the displacement vectors obtained at points of successive GPS campaigns during 2004-2006 and later, we will compute the velocity field over a distance of 30 km (E-W). The network was measured for the first time in May 2004 using the ASTHECH receivers of the Polish group. In particular stations ERIT, KAPA and TAPS (Figure 4) were observed using ASHTECH Zxtreme instruments and ASH701975.01A antennas while the remaining stations were observed using Z-XII instruments and ASH700718B antennas. Station AGTR (Figure 4) was used as the base station. The initial network was expanded during 2005 with the installation of five (5) more stations. All NOA stations were measured using Leica 1200 receivers.

The GPS observations from 2005 and 2006 campaigns were processed in ITRF2000 (Altamini et al., 2002) frame (each daily session separately) using as fiducial points the IGS Italian Permanent Station Matera (MATE) and Greek stations: IGD1 in 2005 and NOA1 in 2006. The Bernese GPS Software v. 4.2 (Hugentobler et al., 2001) was used and special data processing strategy was developed for the local precise network with the following issues and assumptions (Bosy and Kontny, 1998; Bosy et al., 2003):

* Global ionosphere model CODE for a phase ambiguity resolution,

* Antenna phase centres calibrated according to the NGS,

* Troposphere model--the Niell mapping function without a priori model; residual atmosphere zenith delays were estimated for one-hour intervals,

* Precise ephemeris computed by the Centre of Orbit Determination in Europe (CODE) to determine satellite positional data.

All KAPNET positions were resolved with Root-Mean-Square residuals less than 5 mm (horizontal plane; Figure 5). The antenna parameters of the 2005 campaign are given in Table 1. Table 2 presents the ITRF 2000 coordinates of all stations. Figure 5 shows the RMS (Root Mean Square) residuals of the station solutions.

Our first results include coordinates and RMS errors of KAPARELLI local network points for two years 2005 and 2006. They were generated by connecting the daily solutions using the ADDNEQ program (Brockmann, 1996; Hugentobler et al., 2001). Computed ITRF2000 geodetic coordinates ([phi], [lambda] h) referring to their respective epochs as well as their RMS errors are provided in Table 2. The accuracy of determined coordinates ([phi], [lambda] and h) representing un-weighted RMS values of coordinate residuals taken from each year (comparison of station coordinates from each session with respect to the combined solution in mm) is shown in Figure 5. The un-weighted RMS values computed from repeated observations give more realistic accuracy of stations coordinates. The organisation and data processing of repeated satellite GPS standards provide conditions for detecting horizontal movements of the stations at the <5 mm level.

5. DISCUSSION-CONCLUSIONS

a) Dextral shear motion at Kapa1 was indicated. This is found in agreement with non-uniform strain patterns along active normal faults (Roberts and Ganas, 2000). Besides, till now, the TM71 instruments along the Kaparelli Fault show seasonal effects (Figure 3) compatible with seasonal temperature variation.

b) Three (3) similar instruments have been installed in the Perachora peninsula by Maniatis et al. (2003; Figure 1). Given that Holocene fault slip rates at these localities differ by a factor of five (5) or even more it is important to compare 3-D strain measurements in order to estimate interseismic strain accumulation along the two fault zones. Another issue concerns the identification of instrument-induced errors on our measurements and their estimation. The advantage that TM-71 has no electronics parts is counterbalanced by the infinitesimal deformations caused by climatic fluctuations (precipitation, temperature). For example a seasonal effect along the X-axis is visible in the 16-year data series from the Simitli graben in SW Bulgaria (Dobrev and Kostak, 2000).

c) The data processing of repeated satellite GPS standards provide conditions for detecting horizontal movements at our stations at 2-4 mm level. Taking into account the fault movement rate of about 0.5 mm/y, indicated by TM-71 (Figure 3), significant displacement across Kaparelli can be detected by GPS after 4-5 years of observations.

d) The large E-W faults of the Gulf of Corinth slip fast (1-2 mm/yr) and terminate towards the south of the Kaparelli Fault, while the large normal faults of the Parnitha region to the east slip at about five (5) to ten (10) times less (0.2-0.4 mm/yr; Ganas et al., 2004). It is interesting to map this transition in fault slip rates by using the GPS measurements of KAPNET. Our first results (Figure 5) point to an excellent quality of GPS data that will provide stable solutions. A second point concerns the total offset on the Kaparelli fault that is small (< 200 m), while the geological data suggest that it is segmented. So our GPS measurements will differentiate fault slip and strain accumulation among the segments. These observations will also shed light into fault growth processes as Kaparelli is an early phase in the development of large normal faults that involves the merging of two or more faults of differing strikes, rather than the steady lengthening of a single fault segment.

e) The results from the GPS observations will help us establish both the magnitude and direction of geodetic strain and compare it with the Holocene faulting record as published in Pavlides et al., (2003) and Kokkalas et al., (in press). The orientation of the strain axes will be also compared with the configuration of the rupture zones of both the 1981 and the 1999 earthquakes (Figure 4).

ACKNOWLEDGEMENTS

This research was primarily funded by COST Action 625. We are indebted to our COST colleagues for many stimulating discussions. The NOA GPS poles were constructed at the NESTOR workshop in Pylos. We acknowledge reviews by two anonymous referees and useful comments by B. Kostak, G. Stavrakakis, S. Pavlides, I. Koukouvelas, A. Gosar, L. Piccardi, E. Tondi and V. Spina. We thank our NOA colleagues Th. Vourakis, G. Mihalettos, I. Papastamatiou, M. Papanikolaou, and A. Pirentis for help during the field trips. Many thanks are due to E. Skassis for this help with GPS instrumentation. NOA1 data are available from http://www.epncb.oma.be/_trackingnetwork/siteinfo4 onestation.php?station=NOA1_12620M001

[FIGURE 5 OMITTED]

REFERENCES

Altamini, Z., Sillard, P. and Boucher, C.: 2002, ITRF2000: A new release of the International Terrestrial Reference Frame for Earth Science applications, J. Geoph. Res. 107 (B10), 2214, doi: 10.1029/2001JB000561.

Ambraseys, N.N. and Jackson, J.A.: 1990, Seismicity and associated strain of central Greece between 1890 and 1988. Geophysical J. Int., 101, 663-708.

Armijo, R., Meyer, B., King, G.C.P., Rigo, A. and Papanastasiou, D.: 1996, Quaternary evolution of the Corinth Rift and its implications for the Late Cenozoic evolution of the Aegean. Geophys. J. Int., 126, 11-53.

Bosy, J. and Kontny, B.: 1998, Strategy of GPS data processing in local geodynamical networks, Reports on Geodesy No. 9(39), Warsaw University of Technology, Institute of Geodesy and Geodetic Astronomy, 105-113.

Bosy J., Figurski M. and Wielgosz P.: 2003, A strategy for GPS data processing in a precise local network during high solar activity. GPS Solutions, Volume 7, Number 2 Springer-Verlag, 120-129.

Brockmann, E.: 1996, Combination of Solutions for Geodetic and Geodynamic Applications of the Global Positioning System (GPS) PhD. dissertation, Astronomical Institute, University of Berne, Berne, Switzerland.

Cacon, S., Kontny, B., Bosy, J., Cello, G., Piccardi, L., Tondi, E., Drakatos, G. and Ganas, A.: 2005, Local geodynamic researches in Polish Sudetes and the Mediterranean region, Reports on Geodesy, No. 2 (73), 231-244.

Clarke, P.J., R.R. Davies, P.C. England, B. Parsons, H. Billiris, D. Paradissis, G. Veis, P.A. Cross, P.H. Denys, V. Ashkenazi, R. Bingley, H.-G. Kahle, M.-V. Muller and P. Briole,: 1998, Crustal strain in central Greece from repeated GPS measurements in the interval 1989-1997. Geophys. J. Int., 135(1), 195-214.

Dobrev, N., and B. Kostak,: 2000, Monitoring tectonic movements in the Simitli graben, SW Bulgaria. Engineering Geology, 57(3-4), 179-192.

Drakatos, G., Petro, L., Ganas, A., Melis, N., Kostak, B., Kontny, B., Cacon, S. and M. Stercz,: 2005, Monitoring of strain accumulation along active faults in the eastern Gulf of Corinth: Instrumentation and network setup. Acta Geodyn. Geomater., 2, No 1(137), 13-23.

Ganas, A., Pavlides, S. B., Sboras, S., Valkaniotis, S., Papaioannou, S., Alexandris, G. A., Plessa, A., and Papadopoulos, G. A.: 2004, Active Fault Geometry and Kinematics in Parnitha Mountain, Attica, Greece. Journal of Structural Geology, 26, 2103-2118.

Goldsworthy, M., Jackson, J. and Haines A.J.: 2002, The continuity of active fault systems in Greece. Geophysical Journal International, 148, 596-618.

Hubert, A., King, G., Armijo, R., Meyer, B. and Papanastasiou, D.: 1996, Fault Re-activation, Stress Interaction and Rupture Propagation of the 1981 Corinth Earthquake Sequence. Earth & Planet. Sci. Lett., 142, 573-585.

Hugentobler, U, Sacher, S. and Fridez, P.: 2001, Bernese GPS Software Version 4.2, Astronomical Institute, University of Berne, Switzerland.

Jackson, J.A., et al.: 1982, Seismicity, normal faulting and the geomorphological development of the Gulf of Corinth (Greece): the Corinth earthquakes of February and March 1981. Earth & Planet. Sc. Let. 57, 377- 397.

Kokkalas, S., Pavlides, S., Koukouvelas, I., Ganas, A., and Stamatopoulos, L.: in press. Paleoseismicity of the Kaparelli fault (eastern Corinth gulf): evidence for earthquake recurrence and fault behaviour. Bolletino di Geofisica Teoretica ed Applicata.

Kostak, B., and D. M. Cruden: 1990, The Moire crack gauges on the crown of the Frank Slide. Can. Geotech. J., Vol. 27, 835-840.

Maniatis, G., Lempp, CH. and H. Heinisch: 2003, 3D strain monitoring of onshore active faults at the eastern end of the Gulf of Corinth (Greece). J. Geodynamics, 36, 95-102.

Pavlides, S., Koukouvelas, I., Ganas, A., Kokkalas, S., Tsodoulos, I., Stamatopoulos, L., Goyntromichou, C. and Valkaniotis, S.,: 2003, Preliminary palaeoseismological results from the Kaparelli fault (Central Greece). Geophysical Research Abstracts, Vol. 5, 07069, European Geophysical Society.

Roberts, GP. and Ganas, A.,: 2000, Fault-slip directions in central and southern Greece measured from striated and corrugated fault planes: Comparison with focal mechanism and geodetic data. Journal of Geophysical Research, 105 (B10), 23, 443-23, 462.

Athanassios GANAS (1) *, Jaroslaw BOSY (2), Lubomir PETRO (3), George DRAKATOS (1), Bernard KONTNY (2), Marian STERCZ (3), Nikolaos S. MELIS (1), Stefan CACON (2) and Anastasia KIRATZI (4)

(1) National Observatory of Athens, Geodynamic Institute, Lofos Nymfon, Athens 118 10, Greece

(2) Institute of Geodesy and Geoinformatics, Wroclaw University of Environmental and Life Sciences, Grunwaldzka 53, 50-357 Wroclaw, Poland

(3) Geological Survey of Slovak Republic, Jesenskeho 8, SK-040 01 Kosice, Slovak Republic

(4) Department of Geophysics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

* Corresponding author's e-mail: aganas@gein.noa.gr

(Received January 2007, accepted March 2007)
Table 1 Parameters of the KAPNET GPS antennas during
the 2005 (DOY 130, 131) and 2006 (DOY 122, 123)
observation campaigns. Height is in metres.

  2005

   130                                           131

  POINT        ANT. TYPE      h-OBS    h-RED    POINT

  ACLA        ASH700718B      0.8290   0.7654   ACLA
  AGTR       ASH700936D_M     0.7640   0.7262   AGTR
  ERIT      ASH701975.01Agp   0.7810   0.7380   ERIT
  KAPA      ASH701975.01Agp   0.8080   0.7650   KAPA
  TAPS      ASH701975.01Agp   0.8140   0.7710   TAPS
  VILI        ASH700718B      0.8150   0.7514   VILI
  ALYK         LEIAT502       0.7230   0.6672   ALYK
  ASO P        LEIAX1202      0.7500   0.6880   ASOP
  DAFN         LEIAX1202      0.7210   0.6590   DAFN
  DFNL         LEIAX1202      0.7390   0.6770   DFNL
  KALI         LEIAX1202      0.7230   0.6610   KALI

  2006

   122                                           123

  POINT        ANT. TYPE      h-OBS     h-RED   POINT

  ACLA        ASH700718B      0.8350   0.7714   ACLA
  AGTR       ASH700936D_M     0.7640   0.7292   AGTR
  ERIT      ASH701975.01Agp   0.7810   0.7380   ERIT
  KAPA      ASH701975.01Agp   0.8070   0.7640   KAPA
  TAPS      ASH701975.01Agp   0.8120   0.7690   TAPS
  VILI        ASH700718B      0.8200   0.7564   VILI
  ALYK         LEIAT502       0.6910   0.6910   ALYK
  ASOP         LEIAX1202      0.6910   0.6910   ASOP
  DAFN         LEIAX1202      0.6910   0.6910   DAFN
  DFNL         LEIAX1202      0.6910   0.6910   DFNL
  KALI         LEIAT502       0.6910   0.6910   KALI

  2005

   130            131

  POINT        ANT. TYPE      h-OBS    h-RED

  ACLA        ASH700718B      0.8300   0.7664
  AGTR       ASH700936D_M     0.7640   0.7262
  ERIT      ASH701975.01Agp   0.7830   0.7400
  KAPA      ASH701975.01Agp   0.8070   0.7640
  TAPS      ASH701975.01Agp   0.8140   0.7710
  VILI        ASH700718B      0.8150   0.7514
  ALYK         LEIAT502       0.7230   0.6672
  ASO P        LEIAX1202      0.7500   0.6880
  DAFN         LEIAX1202      0.7210   0.6590
  DFNL         LEIAX1202      0.7390   0.6770
  KALI         LEIAX1202      0.7230   0.6610

  2006

   122            123

  POINT        ANT. TYPE      h-OBS    h-RED

  ACLA        ASH700718B      0.8350   0.7714
  AGTR       ASH700936D_M     0.7640   0.7292
  ERIT      ASH701975.01Agp   0.7810   0.7380
  KAPA      ASH701975.01Agp   0.8070   0.7640
  TAPS      ASH701975.01Agp   0.8120   0.7690
  VILI        ASH700718B      0.8210   0.7574
  ALYK         LEIAT502       0.6910   0.6910
  ASOP         LEIAX1202      0.6910   0.6910
  DAFN         LEIAX1202      0.6910   0.6910
  DFNL         LEIAX1202      0.6910   0.6910
  KALI         LEIAT502       0.6910   0.6910

Table 2 The ITRF 2000 coordinates of the KAPNET stations

Point             [phi]              [lambda]

                [o ' '']             [o ' '']

      ITRF2000 EPOCH: 2005-05-10 23:59:45

ACLA   38   14   20.457830  23   10   1.655841
AGTR   38   12   29.119021  23   14   13.982700
ALYK   38   13   34.536100  23   2    42.984761
ASOP   38   17   28.851765  23   29   6.323049
DAFN   38   14   8.585989   23   25   7.455789
DFNL   38   15   31.194095  23   28   16.535688
ERIT   38   12   47.859336  23   20   21.377514
KALI   38   19   18.825944  23   25   14.223037
KAPA   38   13   52.699457  23   13   18.760112
TAPS   38   11   47.745238  23   8    45.103563
VILI   38   10   7.788711   23   18   11.234132

     ITRF2000 EPOCH: 2006-05-02 23:59:45

ACLA   38   14   20.457462  23   10   1.656128
AGTR   38   12   29.118592  23   14   13.982988
ALYK   38   13   34.535574  23   2    42.985050
ASOP   38   17   28.851322  23   29   6.323437
DAFN   38   14   8.585571   23   25   7.456152
DFNL   38   15   31.193592  23   28   16.535760
ERIT   38   12   47.858913  23   20   21.377813
KALI   38   19   18.825917  23   25   14.223237
KAPA   38   13   52.699048  23   13   18.760358
TAPS   38   11   47.744646  23   8    45.103803
VILI   38   10   7.788286   23   18   11.234429

Point     h      RMS      RMS     RMS
                 [phi]  [lambda]   h

         [m]     [mm]    [mm]     [mm]

 ITRF2000 EPOCH: 2005-05-10 23:59:45

ACLA   473.2161  0.5      0.7     3.7
AGTR   578.4204  0.5      0.7     3.7
ALYK   474.9853  0.7      0.7     4.9
ASOP   321.9817  0.5      0.7     3.7
DAFN   533.3963  0.5      0.7     3.7
DFNL   357.5885  0.5      0.7     3.7
ERIT   474.0419  0.5      0.7     3.9
KALI   395.7988  0.5      0.7     3.9
KAPA   340.7526  0.5      0.7     3.7
TAPS   481.9591  0.5      0.7     3.9
VILI   694.3970  0.5      0.7     3.7

     ITRF2000 EPOCH: 2006-05-02 23

ACLA   473.2449  0.5      0.5     3.1
AGTR   578.4606  0.3      0.3     2.0
ALYK   475.0196  0.4      0.5     3.0
ASOP   322.0029  0.3      0.4     2.3
DAFN   533.3879  0.4      0.5     2.7
DFNL   357.6028  0.3      0.4     2.1
ERIT   474.0702  0.3      0.4     2.1
KALI   395.8117  0.3      0.4     2.7
KAPA   340.7809  0.4      0.4     2.4
TAPS   481.9939  0.3      0.4     2.1
VILI   694.4191  0.3      0.3     2.0
COPYRIGHT 2007 Akademie Ved Ceske Republiky, Ustav Struktury a Mechaniky Hornin
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2007 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Ganas, Athanassios; Bosy, Jaroslaw; Petro, Lubomir; Drakatos, George; Kontny, Bernard; Stercz, Maria
Publication:Acta Geodynamica et Geromaterialia
Article Type:Report
Geographic Code:4EUGR
Date:Jan 1, 2007
Words:3548
Previous Article:3-D trend of aseismic creep along active faults in western part of the Gulf of Corinth, Greece.
Next Article:Multi-disciplinary investigations of active faults in the Julian Alps, Slovenia.
Topics:

Terms of use | Privacy policy | Copyright © 2020 Farlex, Inc. | Feedback | For webmasters