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Investigation of recent crustal movements across the Rhine-graben flexure at Basel
Tectonophysics, 29 (1975) 283-287 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
INVESTIGATION RHINE-GRABEN
OF RECENT CRUSTAL FLEXURE AT BASEL
P. BITTERLI-BRUNNER, Geologisch-paliiontologisches
MOVEMENTS
283
ACROSS THE
L. HAUBER and H. FISCHER Institut
der Universitiit
Basel, Base1 (Switzerland)
(Revised version accepted September 16, 1975)
ABSTRACT Bitterli-Brunner, P., Hauber, L. and Fischer, H., 1975. Investigation of recent crustal movements across the Rhine-graben flexure at Basel. In: N. Pavoni and R. Green (Editors), Recent Crustal Movements. Tectonophysics, 29 (l-4): 283-287. Two lines of precise levelling were established and measured across the eastern boundary fault of the Upper Rhine graben at Basel, Switzerland. A brief description of the two lines and an outline of the geology and seismicity of the area are given.
INTRODUCTION
As a contribution to ‘Group 1: Recent Crustal Movements’ of the International Geodynamics Project, a geodetic investigation was initiated in 1971 to detect potential tectonic movements across the eastern boundary fault of the Upper Rhine graben at Basel. The Upper Rhine graben was considered a suitable project for the following reasons: its geology and tectonic history are well known, including information on Quaternary movements; in addition, the noteworthy seismic activity of the rather densely populated area has been realized and recorded for many centuries. In 1971, a programme of precise levelling to be made across the eastern edge of the southernmost Rhine graben was drawn up (Fig. 1). During the summer of 1973 a precision levelling measurement was carried out jointly by the Topographical Survey of Switzerland and the Geodetic Survey of Base1 (Jeanrichard, 1975). GEOLOGICAL
BACKGROUND
The precision levelling carried out at Base1 across this structure zone is aimed at detecting vertical displacements at the eastern boundary fault of the Upper Rhine graben. Here, the continuation of the Black Forest marginal
GERMANY
DI
NKE
L
BERG
Fig. 1. Location
map.
fault is developed as a flexure, the upper bend of which is dissected by faults, resulting in a rather complex structural picture (Fig. 2). Formations of Triassic, Jurassic and Tertiary age are involved. The total vertical downthrow between the Dinkelberg in the East and the graben in the West amounts to about 1000 m in this area. Part of this vertical displacement is probably due to uplift of the eastern block. The main subsidence of the graben occurred during the period from the Late Eocene to the Early Miocene, stretching over a period of some 15 million years. While the Middle Oligocene transgresses along the flexure on the Middle Jurassic, the Tiillinger beds (uppermost Oligocene) themselves are folded by pre-Tortonian movements, forming the Tiillinger syncline to the West of the flexure zone. Later, the movements slowed down considerably, and possibly ceased completely until the Pleistocene, as is evidenced by faulting which has recently been reported upon from some locations in this Rhine-graben area.
285
Tiillinger
Berg
Wlese
Dinkelberg
ESE
WNW
Tiiiiinger
Berg
Maienbtiel
Wlese
kOD
200 0
lurossic S.Betfingen Riehen
lMX)m 400
200
b
~ }
200 0
0
Trioksic ,
,
,
, 1OqOm Bade
After
O.WlTTMANN
Rhine
et al.
Fig. 2. Geological sections across the Rhinegraben
flexure.
SEiSMIClTY
The many earthquakes in the Base1 area in historical times clearly indicate a recent tectonic activity, On October l&h, 1356 one of the most violent earthquakes in the history of central Europe occurred in the southeast comer of the Upper Rhine graben. The city of Base1 was partly destroyed and more than 300 people were killed. The zone of damage extended from Solothurn in the South into the Upper Rhine graben. The magnitude M, was between 6 and 7, the estimated epicentral ~KS-in~nsity I, was 8 or over (I, > 8). Further damaging earthquakes which had their origin in the region of Base1 occurred in the years 1357,1372,1416,1428,1650,1682 and 1721. According to the historical record the eastern border zone of the Upper Rhine
“86
graben shows a substantially zone.
higher seismic activity
than the western border
THE SURVEYED SECTIONS
Of three cross-lines originally suggested, two more or less parallel E--W lines have been selected to the north of the river Rhine. They are at a distance of about 3 km from each other and they were surveyed geodetically during 1973 (Fig. 1). ProfileI
This northern line starts in the East at the German border at an altitude of about 420 m above sea level on Triassic rocks of the Dinkelberg. Following a road towards the SW down to about 350 m a.s.l., the line splits into two legs which run westward across the main faulted zone of the Rhine-graben flexure. From here the profile crosses the alluvial plain of the river Wiese (270 m a.s.1.) as one single line. Then it follows the road upwards to the Ttillinger hill in Germany, where it ends in a loop, at an altitude of 407 m a.s.I., in the Upper Oligocene Tiillinger beds. The profile comprises some fourty fixed points. The length of the lines surveyed totals 7.2 km. Profile 2 The southern line begins in the East, again on Triassic rocks of the Dinkelberg SE of Bettingen at Pt. 456 m a.s.1. From here it follows the Swiss-German border SW-ward, crossing the Rhine-graben flexure, down to the Rhine at Pt. 263. Then it runs along the right bank of the river on alluvial beds, crosses the Rhine over the Wettstein bridge, ending in the City on Niederterrassen gravel beds at 270 m a.s.1. This profile also comprises some fourty fixed points; it has a total length of about 7.3 km with a distance of 5.9 km between the two end points. REFERENCES Barsch, D., Hauber, L. and Schmid, E., 1971. Birs und Rhein bei St. Jakob (Basel) im SpltpleistozB’n und HolozZn. Kegio Basiliensis, 12 (2): 286-315. Fischer, H., 1969. Geologischer Ueberblick iiber den siidlichen Oberrheingraben und seine weitere Umgebung. Regio Basiliensis, 10 (1). Fischer, Ii., Hauber, L. and Wittmann, O., 1971. Erlauterungen zu: Geologischer Atlas der Schweiz, 1: 25,000, Blatt 1047. Basel. Geologische Kommission der S.N.G., 1942. Geologische Generalkarte der Schweiz, scale 1 : 200,000, Blatt 2. Basel-Bern. Herzog, P., 1956. Die Tektonik des Tafeljuras und der Rheintalflexur siidijstlich von Basel. Edogae Geol. Helv., 49 (2): 317-362. Illies, J.H. and Mueller, S., 1970. GrabenProblems; Int. Upper Mantle Project, Sci. Rep. 27.
237 Jeanrichard, F., 1975. Summary of geodetic studies of recent crustal movements in Switzerland. In: N. Pavoni and R. Green (Editors), Recent Crustal Movements. Tectonophysics, 29 (l-4): 289-292. Laubscher, H., 1962. Erdbeben und Tektonik im Rheintal. Verh. Naturforsch. Ges. Basel, 73 (2): 281-289. Maelzer, H. and Strobel, A., 1974. Nivellements und vertikale Krustenbewegungen im Bereich des siidlichen Oberrheingrabens. In: Approaches to Taphrogenesis. Inter-Union Commission on Geodynamics, Sci. Rep. 8 : 88-94. Montandon, F., 1943. Les seismes de forte intensitd en Suisse. Rev. pour l’btude des calamites, Geneve, fast. 18-19 (1942) et 20-21 (1943), 109 p. Pavoni, N., 1974. Maximale Erdbebenintensitlten im Gebiet der Schweiz. Jahresber. 1972 des Schweiz. Erdbebendienstes, Zurich, pp. 164-166. Rothd, J.-P. and Schneider, G., 1963. Catalogue des tremblements de terre du Foss6 rhenan (1021-1965). Veroffentl. Landeserdbebendienst Baden-Wiirttemberg, Stuttgart, 91 p. Sittler, C., 1969. The sedimentary trough of the Rhine graben. Tectonophysics, 8: 543560. Wittmann, O., 1949. Das siidiistliche Ende des Oberrheingrabens. Geol. Rundsch., 37: 24-42. Wittmann, O., Hauber, L., Fischer, H., Rieser, A. and Staehelin, P., 1970. Geologischer Atlas der Schweiz, scale 1 : 25,000, Blatt 1047. Basel.
INVESTIGATION RHINE-GRABEN
OF RECENT CRUSTAL FLEXURE AT BASEL
P. BITTERLI-BRUNNER, Geologisch-paliiontologisches
MOVEMENTS
283
ACROSS THE
L. HAUBER and H. FISCHER Institut
der Universitiit
Basel, Base1 (Switzerland)
(Revised version accepted September 16, 1975)
ABSTRACT Bitterli-Brunner, P., Hauber, L. and Fischer, H., 1975. Investigation of recent crustal movements across the Rhine-graben flexure at Basel. In: N. Pavoni and R. Green (Editors), Recent Crustal Movements. Tectonophysics, 29 (l-4): 283-287. Two lines of precise levelling were established and measured across the eastern boundary fault of the Upper Rhine graben at Basel, Switzerland. A brief description of the two lines and an outline of the geology and seismicity of the area are given.
INTRODUCTION
As a contribution to ‘Group 1: Recent Crustal Movements’ of the International Geodynamics Project, a geodetic investigation was initiated in 1971 to detect potential tectonic movements across the eastern boundary fault of the Upper Rhine graben at Basel. The Upper Rhine graben was considered a suitable project for the following reasons: its geology and tectonic history are well known, including information on Quaternary movements; in addition, the noteworthy seismic activity of the rather densely populated area has been realized and recorded for many centuries. In 1971, a programme of precise levelling to be made across the eastern edge of the southernmost Rhine graben was drawn up (Fig. 1). During the summer of 1973 a precision levelling measurement was carried out jointly by the Topographical Survey of Switzerland and the Geodetic Survey of Base1 (Jeanrichard, 1975). GEOLOGICAL
BACKGROUND
The precision levelling carried out at Base1 across this structure zone is aimed at detecting vertical displacements at the eastern boundary fault of the Upper Rhine graben. Here, the continuation of the Black Forest marginal
GERMANY
DI
NKE
L
BERG
Fig. 1. Location
map.
fault is developed as a flexure, the upper bend of which is dissected by faults, resulting in a rather complex structural picture (Fig. 2). Formations of Triassic, Jurassic and Tertiary age are involved. The total vertical downthrow between the Dinkelberg in the East and the graben in the West amounts to about 1000 m in this area. Part of this vertical displacement is probably due to uplift of the eastern block. The main subsidence of the graben occurred during the period from the Late Eocene to the Early Miocene, stretching over a period of some 15 million years. While the Middle Oligocene transgresses along the flexure on the Middle Jurassic, the Tiillinger beds (uppermost Oligocene) themselves are folded by pre-Tortonian movements, forming the Tiillinger syncline to the West of the flexure zone. Later, the movements slowed down considerably, and possibly ceased completely until the Pleistocene, as is evidenced by faulting which has recently been reported upon from some locations in this Rhine-graben area.
285
Tiillinger
Berg
Wlese
Dinkelberg
ESE
WNW
Tiiiiinger
Berg
Maienbtiel
Wlese
kOD
200 0
lurossic S.Betfingen Riehen
lMX)m 400
200
b
~ }
200 0
0
Trioksic ,
,
,
, 1OqOm Bade
After
O.WlTTMANN
Rhine
et al.
Fig. 2. Geological sections across the Rhinegraben
flexure.
SEiSMIClTY
The many earthquakes in the Base1 area in historical times clearly indicate a recent tectonic activity, On October l&h, 1356 one of the most violent earthquakes in the history of central Europe occurred in the southeast comer of the Upper Rhine graben. The city of Base1 was partly destroyed and more than 300 people were killed. The zone of damage extended from Solothurn in the South into the Upper Rhine graben. The magnitude M, was between 6 and 7, the estimated epicentral ~KS-in~nsity I, was 8 or over (I, > 8). Further damaging earthquakes which had their origin in the region of Base1 occurred in the years 1357,1372,1416,1428,1650,1682 and 1721. According to the historical record the eastern border zone of the Upper Rhine
“86
graben shows a substantially zone.
higher seismic activity
than the western border
THE SURVEYED SECTIONS
Of three cross-lines originally suggested, two more or less parallel E--W lines have been selected to the north of the river Rhine. They are at a distance of about 3 km from each other and they were surveyed geodetically during 1973 (Fig. 1). ProfileI
This northern line starts in the East at the German border at an altitude of about 420 m above sea level on Triassic rocks of the Dinkelberg. Following a road towards the SW down to about 350 m a.s.l., the line splits into two legs which run westward across the main faulted zone of the Rhine-graben flexure. From here the profile crosses the alluvial plain of the river Wiese (270 m a.s.1.) as one single line. Then it follows the road upwards to the Ttillinger hill in Germany, where it ends in a loop, at an altitude of 407 m a.s.I., in the Upper Oligocene Tiillinger beds. The profile comprises some fourty fixed points. The length of the lines surveyed totals 7.2 km. Profile 2 The southern line begins in the East, again on Triassic rocks of the Dinkelberg SE of Bettingen at Pt. 456 m a.s.1. From here it follows the Swiss-German border SW-ward, crossing the Rhine-graben flexure, down to the Rhine at Pt. 263. Then it runs along the right bank of the river on alluvial beds, crosses the Rhine over the Wettstein bridge, ending in the City on Niederterrassen gravel beds at 270 m a.s.1. This profile also comprises some fourty fixed points; it has a total length of about 7.3 km with a distance of 5.9 km between the two end points. REFERENCES Barsch, D., Hauber, L. and Schmid, E., 1971. Birs und Rhein bei St. Jakob (Basel) im SpltpleistozB’n und HolozZn. Kegio Basiliensis, 12 (2): 286-315. Fischer, H., 1969. Geologischer Ueberblick iiber den siidlichen Oberrheingraben und seine weitere Umgebung. Regio Basiliensis, 10 (1). Fischer, Ii., Hauber, L. and Wittmann, O., 1971. Erlauterungen zu: Geologischer Atlas der Schweiz, 1: 25,000, Blatt 1047. Basel. Geologische Kommission der S.N.G., 1942. Geologische Generalkarte der Schweiz, scale 1 : 200,000, Blatt 2. Basel-Bern. Herzog, P., 1956. Die Tektonik des Tafeljuras und der Rheintalflexur siidijstlich von Basel. Edogae Geol. Helv., 49 (2): 317-362. Illies, J.H. and Mueller, S., 1970. GrabenProblems; Int. Upper Mantle Project, Sci. Rep. 27.
237 Jeanrichard, F., 1975. Summary of geodetic studies of recent crustal movements in Switzerland. In: N. Pavoni and R. Green (Editors), Recent Crustal Movements. Tectonophysics, 29 (l-4): 289-292. Laubscher, H., 1962. Erdbeben und Tektonik im Rheintal. Verh. Naturforsch. Ges. Basel, 73 (2): 281-289. Maelzer, H. and Strobel, A., 1974. Nivellements und vertikale Krustenbewegungen im Bereich des siidlichen Oberrheingrabens. In: Approaches to Taphrogenesis. Inter-Union Commission on Geodynamics, Sci. Rep. 8 : 88-94. Montandon, F., 1943. Les seismes de forte intensitd en Suisse. Rev. pour l’btude des calamites, Geneve, fast. 18-19 (1942) et 20-21 (1943), 109 p. Pavoni, N., 1974. Maximale Erdbebenintensitlten im Gebiet der Schweiz. Jahresber. 1972 des Schweiz. Erdbebendienstes, Zurich, pp. 164-166. Rothd, J.-P. and Schneider, G., 1963. Catalogue des tremblements de terre du Foss6 rhenan (1021-1965). Veroffentl. Landeserdbebendienst Baden-Wiirttemberg, Stuttgart, 91 p. Sittler, C., 1969. The sedimentary trough of the Rhine graben. Tectonophysics, 8: 543560. Wittmann, O., 1949. Das siidiistliche Ende des Oberrheingrabens. Geol. Rundsch., 37: 24-42. Wittmann, O., Hauber, L., Fischer, H., Rieser, A. and Staehelin, P., 1970. Geologischer Atlas der Schweiz, scale 1 : 25,000, Blatt 1047. Basel.