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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
265
DOI: 10.4408/IJEGE.2013-06.B-24
THE BERILL FAULT AND ITS RELATION
TO A DEEP SEATED GRAVITATIONAL SLOPE DEFORMATION (DSGSD)
I
ngvar
KRIEGER
(*)
, r
egInald
l. HERMANNS
(**)
, M
arKus
SCHLEIER
(***)
,
F
reddy
X
avIer
YUGSI MOLINA
(**)
, T
HIerry
OPPIKOFER
(**)
, J
an
s
TeInar
rØNNING
(**)
,
T
rOnd
EIKEN
(****)
& J
OacHIM
ROHN
(***)
(*)
University of Erlangen-Nuremberg - GeoZentrum Nordbayern - Erlangen, Germany Now Isofer AG - Knonau, Swizzerland
(**)
Geological Survey of Norway - Trondheim, Norway
(***)
University of Erlangen-Nuremberg - GeoZentrum Nordbayern - Erlangen, Germany
(****)
University of Oslo - Oslo, Norway
tical step in high mountain terrain have often been
discussed to be either related to faulting or to deep
seated gravitational slope deformation (T
HOMpsOn
et
alii, 1996; H
IppOlyTe
et alii, 2006; l
I
et alii, 2010).
The slope of the investigation area shows a promi-
nent 1.5 km long linear feature, that strikes NNE-
SSW and therefore in a 30 degree angle with the SE
facing slope. It forms a 3-4 m high step in the topog-
raphy and was previously discussed as a Holocene
reverse fault called the "Berill fault" (a
nda
et alii,
2002). Only on the western side of the fault a mas-
sive rock slope instability has developed. Here oc-
cur slope parallel, up to 20 meter deep up-hill facing
scarps (counter scarps) with active rock fall and shal-
low translational sliding of single rock blocks and
unconsolidated rock (e.g. shallow landslides). East
of the lineament called the “Berill fault” no slope
deformation is visible. Hence the fault seems to be a
limiting factor for the slope instability.
In order to better understand the relation of the
slope deformation with the proposed Holocene re-
verse fault, an intensive structural analyses of the
slope and electric resistivity profile measurements
along the valley floor were implemented and the
deformation was monitored over the past 5 years
with differential Global Navigation Satellite System
(dGNSS) surveys. The investigation area is located
on the south-east exposed slope of the Middagstin-
den mountain right above the Berrilvatnet lake in the
Møre og Romsal county in West Norway (Fig. 1) and
ABSTRACT
Within the Innfjorddalen valley (Møre og Roms-
dal, Norway) a 1.5 km long linear NNE-SSW striking
feature, forming a 3-4 m high step in the topography,
occurs on the SE facing slope of the Middagstinden
mountain and was previously discussed as a Holocene
reverse fault, called the "Berill fault". Our intense
structural field mapping and a high resolution digital
elevation model based on LiDAR data derived from
airborne and terrestrial laser scanning indicate that the
"Berill fault" is a normal fault that has the orientation
of the collapse of the Caledonian orogen, that is today
reactivated as a limiting structure of a Deep Seated
Gravitational Slope Deformation (DSGSD). Differ-
ential Global Navigation Satellite System (dGNSS)
surveys over the instability indicate velocities of the
DSGSD of ca. 0.6 cm/yr. Three electric resistivity pro-
files on the valley floor attest that the fault is a structure
with regional extend. Three trenches with a total length
of 100 m parallel to the electric resistivity profiles al-
though down to glacial deposits or the underlying
bedrock do not indicate any Holocene activity of the
fault. Hence reactivation of the fault by the DSGSD
produces the linear feature oblique to the slope.
K
ey
words
: normal fault, rock slope instability, LiDAR, kine-
matic analyses, Western Norway
INTRODUCTION
Several km-long linear features that build a ver-
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International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
35 locations were taken. Furthermore the main fea-
tures and the limiting structures in the instability were
mapped in order to estimate the size of the individual
blocks (Fig. 1 and 2).
Supplementary data for structural analyses was
gained from airborne- and ground based LiDAR-
(Light Detection and Ranging) data in order to create
a high resolution digital elevation model (DEM). To
create a DEM by terrestrial laser scanning (TLS) the
site was scanned with the long range ILRIS Optech
3D Scanner (O
pTecH
, 2008) from several positions
with different lines of sight (Fig. 1) to get a prefer-
ably dense 3D point cloud. To keep the vegetation as a
disturbing factor to a minimum only the last reflected
impulse of the pulsed laser was recorded. The LiDAR
point clouds were cleared of disturbing factors like
vegetation and georeferenced in the PolyWorks soft-
ware (I
nnOvMeTrIc
, 2011; O
ppIKOFer
et alii, 2012). In
addition, to gain a better overview over the site and
its prominent structures and to improve the field in-
vestigations (mapping and structural measurements)
detailed Orthophotos as well as a DEM based on
airborne laser scanning (ALS) with a resolution of 2
meters were used. The DEM suits very well as input
data for differently exposed hillshades for a better un-
derstanding and identifying of the large morphologi-
cal structures in the instability.
STRUCTURAL ANALYSES
The data collected in the field and the values gained
by the Coltop3D analyses were stored and analysed
with the software Dips6.0 (r
OcscIence
, 2012) The ori-
entations of the planes are displayed by its great circles
and pole points in the Stereonet (lower hemisphere,
equal area). Furthermore, kinematic tests for planar and
wedge sliding as well as direct flexural toppling were
performed to determine the possible failure modes.
In order to analyse the orientation of the dis-
continuity sets in the DEMs the Coltop3D software
(T
erranuM
, 2011) was applied (
JabOyedOFF
et alii,
2007). The software computes surface normals out of
the point cloud DEM and provides them with an ori-
entation-specific colour. In the next step, by selecting
surfaces with the same colour, Coltop3D was used to
illustrates the orientations of the defined planes in a
spherical projection (lower Stereonet) and to export
the results as dip and dip direction in a text file (O
p
-
pIKOFer
et alii, 2012).
herein it is described as the “Berill instability”. The
instable slope is part of the Innfjorddalen, a glacial
U- valley, where several post glacial mass move-
ments have taken place (s
cHleIer
et alii, this issue).
GEOLOGICAL SETTING
The Berill instability is located in the Western Nor-
wegian Gneiss Region (WNGR). The bedrock of this
area consists mainly of proterozoic gneisses with a mag-
matic origin, which is locally covered with oceanic and
continental sediments. The deformation and metamor-
phisation of the neo- and mesoproterozoic rocks took
place during the Caledonian orogeny (g
anerød
, 2008).
In the geological map sheet the gneisses are described as
undifferentiated and locally migmatitic in composition
(T
veTen
et alii, 1998). The most prevalent rock types
in the WNGR are tonalitic and granodioritic gneisses
(H
acKer
et alii, 2010). The bedrock disclosed in the in-
vestigation area is marked of quartz-dioritic gneiss with
a sporadically well distinct foliation. Locally migmatitic
structures are present (T
veTen
et alii, 1998).
METHODS
DATA USED
A detailed structural field mapping over the
whole investigation area with rock outcrops was un-
dertaken and about 1500 structural measurements at
Fig. 1 - Orthophoto of the Berill instability (NGU) showing
the different observation points for field data, TLS
data and dGNSS measurements, the position of the
trenches and the electric resistivity profiles and the
morphological trace of the fault; The investigation
is limited to the western part of the instability with
rock outcrops, since the rest is covered by surficial
glacial deposits that do not allow the implementa-
tion of structural analyses of the bedrock
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THE BERILL FAULT AND ITS RELATION TO A DEEP SEATED GRAVITATIONAL SLOPE DEFORMATION (DSGSD)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
267
a movement is expected to be significant when it is
larger than the uncertainty. Because of large height
differences between the rover points and the fix point
as well as annual systematic trends from un-modelled
meteorological effects, the vertical uncertainty is
much higher than the horizontal (b
öHMe
et alii, 2012)
and hence must be interpreted carefully.
GEOELECTRIC
Three 2D resistivity profiles were measured in the
valley bottom (Fig. 1) using the Lund system (d
aHlIn
,
1993) gradient electrode configuration and an ABEM
SAS Terrameter 4000 (ABEM, 1999). Electrode separa-
tion was two meters (profile 1 and 2) and five meters
(profile 3) giving a penetration depth of 25 and 60 meters
respectively. This method has proven to be a powerful
tool for mapping of drift deposits and fracture zones in
bedrock (s
Olberg
et alii, 2008; r
ønnIng
et alii, 2009).
For a better understanding of the possible move-
ments within the rock, a comprehensive recording of
persistance, spacing and roughness of the discontinu-
ity sets according to W
yllIe
& M
aH
(2004) was ac-
complished during the fieldwork.
DISPLACEMENT MEASUREMENTS
Displacements within the instability have been
measured yearly by dGNSS surveys since 2008 (no
measurement possible in 2012 because of bad weather
conditions). Therefore three rover points were in-
stalled in the apparent instable parts of the mountain
slope and one fixed point (Fig. 1) in a stable part above
the main scarp, to receive a network of vectors which
shows the point movement relative to each other. For
this method, uncertainties in horizontal directions of
3-6 mm and in the vertical direction of 10-20 mm are
assumed (H
erManns
et alii, 2011). Thus in this paper
Fig. 2 - Hillshade of the Berill instability with the different kinematic areas, morphological trace of the fault the main scarp
and the relative movement of the dGNSS rover points
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International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
UPPER WESTERN PART (AREA 5)
Area 5 shows one coherent block with defined lat-
eral limits and many single, randomly distributed out-
crops of the bedrock at the western and frontal mar-
gins that are surrounded by large blockfields. Since
the major part of blocks in the deposits does not show
repositioning structures (angular –partly very angular
blocks) and there are highly fractured outcrops within
the blockfields, the blocks are suggested to come from
fragmentation on site but not by rock falls from above.
The horizontal displacements at the main scarp of
the rock slope instability above area 2 and area 5 to
the moving mass below is approximately 50 meters
while the height of the scarp amounts to ~ 60 meters.
The main scarp forms the back bounding limit both of
area 2 and area 5.
STRUCTURAL ANALYSES
By analysing the structural data of the field and
the DEMs, four main discontinuity sets have been
identified (Tab. 1). The persistence, spacing and
roughness descriptions refer to the classification of
W
yllIe
& M
aH
(2004).
FOLIATION (JS)
The foliation JS plunges with a mean dip/dip direc-
tion of 156/47 (field value) and varies over the whole
area of the instable slope. In area 2 and area 5 the folia-
tion forms distinct discontinuity surfaces with a high
persistence, a close-moderate spacing and shows very
little variability in the orientation. The surface of the
foliation is here smooth and planar-undulating and both
the main scarp and the frontal limit of area 2 are formed
by the foliation. In the lower parts, especially in the
counter scarps in area 2,the occurrence and the orienta-
tion are not constant. Here, the orientation of the folia-
tion (dip direction) varies between NNE and SSW with
RESULTS
MORPHOLOGY ON SLOPE
Based on the field mapping and ALS as well
as Orthophoto analyses, four main areas (area 2-5)
within the rock slope (Fig. 2) can be distinguished
showing different types and/or amount of deforma-
tion. Similar deformation is suggested by counter
scarps in surficial deposits E of the described rock
slope and NW of the linear feature described as
"Berill fault" (area 1).
EASTERN PART COVERED BY SURFICIAL
DEPOSITS (AREA 1)
This area shows 3-4 meter deep depressions,
which strike in the same direction as the counter
scarps and the main scarp and deform the surficial
deposits and limit towards the fault. Furthermore
lateral morains associated to younger Dryas glacia-
tions can be found in this part of the slope instabil-
ity. The fault strikes NNE-SSW and can be traced
morphologically by a convex lineation along the
slope which is 3-4 meters high and 1.5 km long but
disappears in the valley.
UPPER MIDDLE PART (AREA 2)
Area 2 shows one coherent block with active
rock fall at the lateral and frontal margins. Here
large block fields have developed with up to several-
meter- sized blocks.
LOWER MIDDLE PART (AREA 3)
Area 3 displays very prominent, up to 20 meter
deep uphill facing scarps (counter scarps) with regular
rock fall at the rockfaces. Hence the scarps are filled
with meter sized blocks, so the real depth is masked.
The distance between the individual rockfaces varies
between 10 and 50 meters.
LOWER WESTERN PART (AREA 4)
Area 4 is characterised by large block fields with
local repositioning structures. Where the blocks get
smaller and mix with soil, surficial mass movements
(e.g. shallow landslides) are present. Outcrops of the
bedrock can only be found in some few parts and even
then they are highly weathered and fractured. The
transition to area 5 shows an accumulation of outcrops
imbedded in large block fields.
Tab. 1 - Summary of the main discontinuity sets. The ori-
entation data are presented as dip/dip direction
with ± 1σ variability in degrees; the spacing, per-
sistence and roughness descriptions refer to the
classification of W
yllie
&M
ah
(2004)
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THE BERILL FAULT AND ITS RELATION TO A DEEP SEATED GRAVITATIONAL SLOPE DEFORMATION (DSGSD)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
269
ment of 19 mm since 2008, while Berill2 and Berill3 in-
dicate a movement towards SSW (194° and 193°) with
a displacement of 14 mm (Berill2) and 19 mm (Berill3)
since 2008. Especially Berill1 and Berill2 show high
variations in the east-west displacement, while Berill3
moves mainly constantly towards SSW (Fig. 3)
GEOELECTRIC
All resistivity profiles show low resistivity on the
surface and higher resistivity at few meters depth. In
addition, in all profiles there is one pronounced zone
of low resistivity that separates areas of high resistiv-
ity that is ca. 10 m wide and dips either vertical or in
the proposed dip direction of the fault. A second less
pronounced zone of lower resistivity runs parallel to
the former zones (Fig. 4).
DISCUSSION
GENESIS OF THE FAULT
The fault plane shows significant quartz-feldspar
remineralisation with quartz/feldspar lineation that in-
dicates that the fault was active in depth prior to exhu-
mation to its present position. Moreover frequent break
offs indicate a down-dip direction and hence a normal
fault process (Fig. 5). The orientation of the lineation is
parallel to the direction of the collapse of the Caledo-
nian orogen. The low resistivity zone within the valley
dips in the same direction and is thus interpreted to rep-
resent the prolongation of the fault in the valley. NGU
opened trenches along the resistivity profiles that went
shallower inclinations between 5° and 40° with higher
spacing and lower persistence values than in the upper
area. This is because of folding in centimeter but also in
meter scale with a fold axis towards the east.
JOINTS (J1, J2)
Two prominent joint sets are developed (J1, J2)
that are both steep dipping with mean dip/dip direction
values of 74/320 for J1 and 78/045 for J2 (field val-
ues). The spacing is wide – very wide, the persistence
is high and the discontinuity surfaces are rough, planar,
occasionally undulating. Most of the prominent struc-
tures like big fractures, cracks or lineaments visible
in the field and on the DEM develop along these joint
sets and single blocks or outcrops in the instability are
limited by J1 and J2 or a combination of both. At the
main scarp the occurrence of these joint sets is not as
frequent as in the deforming parts and their persistence
is much lower. This gets confirmed both by field obser-
vations and the analyses of the DEMs.
FAULT PLANE (JF)
The fault plane dips with a mean dip/dip direc-
tion of 44/270. The surface shows a quartz–feldspar
remineralisation with lineation and frequent break
offs that indicate normal fault movement. These line-
aments do not occur continuously on the surface of
the plane and the planes are partly undulated with
varying orientations. Therefore the fault plane might
follow a pre-existing discontinuity that was used as
a preconditioned zone of weakness in the course of
faulting. Because of its relative shallow orientation
dipping into the mountain slope it can not be found
in the DEMs, but the field investigation yield high,
occasionally even very high persistence values. The
spacing varies very much depending on the area. In
some parts the outcrops of the surface recur in meter
scale, in other parts it does not exist and in the lower
parts (counter scarps) it plunges about 16° shallower
than further up on the slope.
DISPLACEMENT MEASURMENTS
All rover points show a significant horizontal move-
ment towards the south with a mean displacement rate
of ~0.6 cm/year. The vertical movements over the last
four years are not higher than the uncertainty and there-
fore are not discussed. The rover point Berill1 moves
straight towards the south (176°) with a total displace-
Fig. 3 - Horizontal displacement rates of Berill 1 and
Berill 2 since 2008
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International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
down into glacial deposits or down to the basement. No
fault offsets or any soft sediment deformation features
indicating seismic activity within the trenches were
observed. Thus we interpret that the fault represents a
fault active during the Caledonian collapse that has not
been seismically reactivated in post glacial times.
INFLUENCE OF THE FAULT TO THE SLOPE
DEFORMATION
The field data and the additional TLS data show, that
the main scarp is mainly formed by the foliation JS which
plunges with a mean value of 52/154 (data taken in the
field at the main scarp) and therefore does not daylight on
the slope. However groove marks (Tab. 1) on the main
scarp indicate a rockslide towards SSE. As the foliation
is not daylighting, this movement becomes only possible
because the foliation intersects with the fault plane form-
ing an intersection lineament with the orientation 22/205
(Fig. 6). This orientation is 50° obliquely towards the ori-
entation of the slope that strikes N 065° E with an aver-
age slope angle of 45°. The orientation of the sliding rock
mass therefore moves out of the slope as a wedge failure
with an angle of 50° relative to slope direction producing
a positive offset along its SE boundary forming a step
in the rilief similar to thrusting along the fault plane in
an eastward direction (Fig. 5). Thus the Caledonian fault
gets reactivated through the slope instability in form of an
"apparent reverse fault". This direction is identical with
the movement direction documented with the dGNSS
rover stations Berill 1-3. Because the fault and the folia-
tion are not present over the entire slope and their orien-
tations are variable, also other deformation styles have
developed on the slope in various sectors.
AREA 1
The bedrock of this area is covered by surficial
glacial deposits and therefore it was neither possible
to collect applicable structural data nor to install rep-
resentative dGNSS points. But since area 1 also shows
depressions, which strike in the same direction as the
counter scarps in area 3, this part of the slope might
follow a similar slope deformation process.
AREA 2
This coherent block has a surface area of 130.000
m
2
and is delimited by the joint set J1 in the front and
Fig. 4 - Resistivity results along profile P1; low resistivity (blue colours) represent peat material at the surface and a 10 meter
wide fractured zone in the bedrock dipping towards the west
Fig. 5 - Pictures of the fault plane JF taken in the field
a) lineation plunging 33/241; b) breakoffs on the
hanging wall of the fault plane indicating a down
dip direction
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THE BERILL FAULT AND ITS RELATION TO A DEEP SEATED GRAVITATIONAL SLOPE DEFORMATION (DSGSD)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
271
investigations we summarize:
1. The fault plane is supposed to be a pre-existing
by J2 at its lateral limits. This block moves SSE along
the foliation as shown by the groove marks at the back
bounding scarp and therefore nearly in direction of
the inclination of the slope. This movement builds up
stress in the lower part of the slope in area 2.
AREA 3
dGNSS measurements and the kinematic analy-
ses show, that area 2 is moving SSW that is therefore
parallel to the intersection line of JS and JF (Fig. 6).
However, as the foliation is less developed in this
area deformation is also taken up by J1 by toppling
towards SE (Fig. 7). This produces the counter scarps
and might explain the varying east-west displacement
rates of Berill1 and Berill2, which are installed at the
top of the rock faces of the counter scarps. An SE di-
rection of toppling and in combination with the SSW
direction of wedge sliding on the intersection line
of the foliation and the fault of this part of the insta-
ble slope results in the observed S movement of the
dGNSS points. Area 2 and area 3 are described here
as two different areas since the kinematic processes
differ from each other, but still both areas outline one
coherent block in the hillshade.
AREA 4
In area 4 no dGNNS point could be installed,
because there are neither coherent blocks nor unfrac-
tured outcrops. The few existing outcrops are highly
fractured with wide opened discontinuities likely re-
lated to high strain rates from the surrounding coher-
ent blocks that “push” on this part of the slope.
AREA 5
The dGNSS measurements of the rover point
Berill 3 and the Stereoplots indicate that the coherent
block in the upper western part moves SSW and there-
fore differs from the moving direction of the upper
eastern block. This block is separated from the block
of area 2 along the joint set J2 and it moves parallel
to intersection line of JS and JF towards SSW. The
highly fractured outcrops of the bedrock at the west-
ern and frontal margins are assumed to be the result of
varying movement directions of surrounding blocks.
CONCLUDING REMARKS
In conclusion after our thorough structural map-
ping in combination with dGNSS and geophysical
Fig. 6 - a) wedge sliding along the intersection line of the
foliation JS and the fault JF; The input data are
mean values of JF and JS taken in the lower parts
(area 2) of the slope instability where the wedge
developed; because of the slickensided surface of
the fault and the smooth surface of the foliation
the friction angle is estimated to be as low as 20°.
The also plot shows the direction of the dGNSS
rover points Berill1-3; b) field photo of the sliding
on the intersection line between JF and JS with
measured value of 21/201 (plunge/trend)
Fig. 7 - Toppling along the joint set J1 with the directions
of the dGNSS rover points Berill1-2; the friction
angle is with 25° higher than in Figure 3 because
of a rougher discontinuity surface; the slope has a
mean orientation of 45/155 (dip/dip direction)
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International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
5. Due to different orientations of the slope and the
wedge, the sliding rock mass produces a posi-
tive offset along its SE boundary and reactivates
the fault plane locally in form of an “apparent
reverse fault”.
6. As the fault plane and the foliation plane do not
occur constantly over the unstable slope, also
other deformation styles developed on the slope,
which are all terminated by the joint sets J1 and J2
and result in localized toppling towards the SE.
ACKNOWLEDGEMENTS
This investigation was funded by the Geological
Survey of Norway, which contributed both with phys-
ical and intellectual work very much to this paper.
discontinuity which was exploited as a weakness
zone in the course of faulting.
2. The quartz-feldspar remineralisation with linea-
tion and break offs indicate a normal fault process
towards the west.
3. Since the fault is parallel to the direction of the
collapse of the Caledonian orogen and there was
no evidence of fault deformation in the soft sedi-
ments in the trenches, we assume that the fault
was active during the Caledonian collapse and
was not reactivated in post glacial times.
4. The fault plane intersects with the foliation forming
a wedge with an intersection lineament plunging
SSW that takes part of the deformation. This direc-
tion coincides with dGNSS measurement of Berill3.
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