Page 6 - Ragg_et_al-1999-Tectonics

674 RAGG ET AL.: TECTONIC STRESS IN SICILY

Table 1. StressOrientationin 22 Wells DeducedFromBoreholeBreakoutAnalysis

Bottom-TopLogInterval, HeightAboveSea Latituded, eg Longituded,eg SHmax+/- Standard

Name m Level, m Deviation Quality

SE Sicily, Hyblean Plateau

Cassibile 1512-323 60 36.9809 15.2308 166ø+/- 13.7ø B
Capo Negro 2126-240 34.1 36.9401 15.1217 131ø+/- 12ø A
Bimmisca 2809-305 31.3 36.8094 15.1244 154ø +/- 11.5ø B
Cozzo Scalia 2911-392 42.3 36.7751 15.0668 152ø+/- 15ø B
Carrubo 3182-147 62.3 36.7673 15.0111 144ø+/- 52ø D
SanBartolo 2615-200 208.4 36.8664 14.5887 158ø+/- 17ø B

Vittoria Ovest 2407-511 SE Sicily,Foredeep 48ø+/- 38ø D
Biddine 2350-620 141o +/_ 31o D
ContradaUlmo 2524-301 159.7 36.9458 14.5414 107ø +/- 57ø D
Margi 1739-704 244.9 37.0578 14.5548 147ø+/- 47ø D
Ursitto 3825-345 223.8 37.1114 14.4817 113ø +/- 42ø D
126.4 37.3135 14.7200
Settefarine 4719-2500 20ø+/- 13ø A
Manfria 4350-2903 124.3 37.1800 14.4186 16ø +/- 15ø B

Angelo 4100-3100 SE Sicily, Gela 36ø+/- 11.6ø B
Ramacca 1267-247 66ø +/- 13ø B
37.1203 14.3031
Simeto 979 -197 62ø+/- 25ø C
Dittaino 1160 -300 16.4 37.1167 14.1640 - E
Chiesa 1100 -296 42ø+/- 11o B
SESicily,Mt. JudicathrustsandGelaNappe
Menfi 1677-292 120ø+/-35 ø D
Triglia 2414-258 489 37.4748 14.5417 1ø+/- 28ø C
Mozia 2493 -449 138.8 37.4481 14.7444 120ø+/- 20ø C
Corvi 1280-300 148ø+/- 22ø C
SE Sicily,CataniaPlain

14.2 37.4268 15.0431
30.2 37.4159 14.9585

37 37.4310 14.9140

WesternSicily

99.3 37.6045 12.9828
23.7 37.6791 12.5811
16.3 37.8882 12.5304
57 37.8445 12.5616

Thewellsareorderedin a regionagl eologicaclontextT. herangeof theavailablecaliperdata,locationabovesealeavel,
longitudela, titudeo, rientatioonf SHmaxwithstandarddeviationa,nda qualityfactor(accordintogZobacketal. [1985])aregiven.

Angelo (well 14), drilled throughthe Mount Judicathrusts, 1986; Ward,1994].This orientationis roughlyparallelto

andRamacca(well 15), locatedon the frontalGela Nappe,is the WesternEuropeanstresstrend and is consistenwt ith the

subparallel to the orientations found in the Catania Plain opening of the NW-SE trending Pantelleria Rift in a

(wells 16 and 18). This suggestsa slightclockwiserotationof transtensionarel gime[Reutherand Eisbacher,1985; Gardiner

SHmaxfrom N-NNE in the frontal Gela Nappeto NE in the et al., 1995].

Catania Plain. Even though they are located on different 2. The wells drilled throughthe Gela Nappeinto the

geologicunits, the wells Angelo and Ramaccaare in close underthrustinagnd NW downbendingHybleansubstratum

proximityandgive similarresults(Table I andFigure7). This [GrassoandReuther,1988; Ben-Avrahamet al., 1995]are
similarity may testify that the present-dayregional stress characterizebdy a NNE-SSWSHmaxorientationro, ughly
orientationat depth is coherentand is not very sensitiveto orthogonatol theaxisof the PantelleriaRift Systemin the
lithology.
Strait of Sicily. The wells of the Mount Judicaarea and the

The combinationof the data obtained from the breakout frontal Gela Nappe, located to the north, exhibit a NE

analysiswith the stressdatafromthe WorldStressMap, orientatioonf SHmax.To theeast,in theCataniaPlain,a NE-

taking into account the geotectonic context, can be SWorientatioonf SHmaxis obtainedT.hisis subparallteol
summarized as follows:
the faultsflankingthe grabenswhich dissectthe northern
1. A nearly NNW (148ø) orientationfor SHmax is detected marginof the HybleanPlateau[Lentiniet al., 1984].
ontheHybleanPlateau(Figure1).Thiscouldbeinterpretetdo ThereforSeHmaxis subparalletol therecentnormaflaults,
resultfrom plateboundaryforcesdue to the convergent whichdissecttheflexurednorthermn arginof theHyblean
motionof the African plate versusEurasia[Grassoet al., Plateaua,ndcorrespontdostheintermediapterincipasltress