MAIN ACTIVE FAULTS FROM ROMANIA. Part III: FAULT SYSTEMS FROM DACIA TECTONIC UNIT

Abstract

The main target of this paper is to established a correlation between the seismicity of the Western part of Southern Carpathians (Romania) and the active tectonic (faults systems) of the area, the second target is to create a specific database of the faults (ROmanian DAtabase of SEismogenic Faults-RODASEF) in SHARE manner, for seismic hazard assessment process. In the studied area, we highlit the main faults form Hateg Basin, Moldova Noua-Oravita Basin, Caransebes-Orsova basin (Teregova) and Orsova-Mehadia-Cornereva faults system, which generate seismic sequences such as:

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Romanian Reports in Physics 73, 710 (2021)
MAIN ACTIVE FAULTS FROM ROMANIA.
Part III: FAULT SYSTEMS FROM DACIA TECTONIC UNIT
M. DIACONESCU
1,2
, C. GHITA
1
, I.A. MOLDOVAN
1
, E. OROS
1
,
E. G. CONSTANTINESCU
1,3
, M. MARIUS
1
1
National Institute for Earth Physiscs, 12 Calugareni str, Magurele, Romania
2
Romanian Society of Applied Geophysics, 1 N. Balcescu Bd., Bucharest, 010041
3
20c Prospectiuni S.A., Coralilor, Bucharest, 013326
E-mail: diac@infp.ro; cristi.ghita@infp.ro; irenutza_67@yahoo.com
Received August 10, 2020
Abstract. The main target of this paper is to established a correlation between
the seismicity of the Western part of Southern Carpathians (Romania) and the active
tectonic (faults systems) of the area, the second target is to create a specific database
of the faults (ROmanian DAtabase of SEismogenic Faults-RODASEF) in SHARE
manner, for seismic hazard assessment process. In the studied area, we highlit the
main faults form Hateg Basin, Moldova Noua-Oravita Basin, Caransebes-Orsova basin
(Teregova) and Orsova-Mehadia-Cornereva faults system, which generate seismic
sequences such as: 2002 Moldova Noua, 1991 Mehadia-Baile Herculane, 2014 Teregova,
2011 and 2013 Hateg seismic sequences.
Key words: focal mechanism, faults, seismogenic sources.
1. INTRODUCTION
The goal of this paper is to define and describe the faults, from the Western
part of Southern Carpathians (Romania) belonging to the Dacia tectonic unit. The
paper used the Database of Individual Seismogenic Sources – DISS methodology, of
the National Institute of Geophysics and Volcanology, Rome, Italy. The description
of the faults is in terms of geometrical parameters under a permanent updating [1, 2].
The rationales behind DISS are fully explained in [1–3] and [4]. The Seismic Hazard
Harmonization in Europe-SHARE project used DISS methodology to create European
Database of Seismogenic Faults (EDSF). Other projects which use the same
methodology are European Research Infrastructure on Solid Earth – EPOS and
Assessment, Strategy and Risk Reduction for Tsunamis in Europe – ASTARTE.
The DISS methodology was used in [5], an overview of the seismogenic
sources of Northern Italy and Western Slovenia, in [6] the description of the
seismotectonics of the Po Plain, [7] the study of the seismogenic sources of the
Adria and the evaluation of the slip rates of the fold belt from the Dinarides [8] and
of the Po Plain [9]. Also this methodology was used to creat The Greek Database
of Seismogenic Sources [10].

Article no. 710 M. Diaconescu et al. 2
This paper is a continuation of another two articles which higlights the active
faults from Dobrogea and Western basin of the Black Sea in terms of DISS
methodology by [11] and [12].
2. GEOTECTONIC SETTING
The studied area is situated in Southern Carpathians and consists of two
main seismological domains: Hateg-Strei Basin and Danubian Domain as defined
by [13]. Three main tectonic units are described in these areas: Median Dacides
(Getic and SupraGetic nappes), Marginal Dacides (Danubian Unit) and External
Dacides (Severin nappes), also are present post tectonics cover, post tectogenetic
elements and prealapine igneous rocks (Fig. 1).
Fig. 1 – Geotectonic map of the area of interest. Tectonic after [14].
The current tectonic structure of the Southern Carpathians is the combined
result of a main rotation movement towards the north and a lateral one, to the right,
in which the tectonic units of the Internal and External Dacides, the Danube around
of the Moesian platform took part. Strike slip-type deformations have played an
important role in the tectonic development of the region. Another result of this
tectonic regime is the formation of intra mountain pull-apart basins such as: Hateg

3 Main active faults from Romania. Part III Article no. 710
Basin, Caransebes-Mehadia Basin, Orsova Basin, Bozovici Basin, Sichevita Basin,
and Oravita Basin.
Hateg–Strei tectonic system is situated in the western part of the Southern
Carpathians, and consists of two intermountain, post orogenic basins, the Hateg
Basin and the Strei Basin separated by a threshold nearby Hateg city. The Hateg
Basin is located between Retezat Mountains to south, Sebes Mountains to the east,
Poiana Rusca Mountains to the west and to the north by Strei basin [14]. Sedimentary
deposits belong to the interval Paleogene-Miocene and ends with Badeniano-Sarmatian
deposits, but not as a continuous sedimentary suite, showing major stratigraphic
hiatus in the Eomiocen. Consequently, there are two cycles of sedimentation:
Paleocene-Eomiocen first and second Meso-Neomiocen. The basement consists of
Sebes-Lotru crystalline schist’s series. From a tectonic point of view, this system is
affected by some thresholds at basement level and delimits more zones with
different evolution for a short period of time [14].
Fig. 2 – Tectonic map of the area, after [14].
The Hateg-Strei Basin is segmeted by faults with NW-SE to E-W orientation.
The Hateg-Strei system is characterized by ruptural tectonic superimposed to a
monoclinic structure, in which the terms are succeeding from the oldest to the
newest, from ENE to WSW. This ruptural tectonic is defined by a subhercinic age
or later. Also, the system is affected by Alpine tectonics through ruptural disjunctive
dislocations and subordinate by the plicative dislocations affecting both the pre-
Mesozoic basement and Mesozoic-Tertiary sedimentary deposits. The NE-SW

Article no. 710 M. Diaconescu et al. 4
system faults are the main faults in the area, more important than the faults of the
second system (NW-SE), affecting both the region surrounding basin and the basement
of the basin [15]. Throughout such system of fractures, oriented NE-SW, basin formed
by dipping some of the basement blocks with fault plane dipping to the south east
and a NE-SW orientation, such as Hateg-Sarmisegetusa Regia Fault (Fig. 2).
Danubian Domain is segmented by a NE-SW to E-W oriented faults and
represent Carpathian fault system [14]. These are mainly thrusts which delinate
WNW verging nappes inside Median and Marginal Dacides (such as Sichevita-
Retezat thrust, Fig. 2) or vertical fault such as Oravita-Moldova Noua Fault system
(Fig. 2), Cerna-Jiu fault system (Fig. 2). Ignous rocks are distributed through basement
formations being a associated with deep fault system in the Alpine time (Fig. 1).
Neotectonic age is characterized by vertical movements in these period forming
intramountains depressions (basins) filled with neogene sediments which covered
the pre-exting structures. Basin like these are: Caransebes-Mehadia Basin, Orsova-
Bahna Basin, Sichevita Basin, Bozovici and Oravita Basin.
3. SEISMICITY
The area of interest Hateg Basin and Danubian Domain is known as a zone
of moderate crustal earthquakes with magnitudes exceeding M
w
value 5.0, but not
exceeding the M
w
value 5.6. The seismological characteristic is the production of
seismic sequences in some areas. One area is considered in Hateg Basin and three
areas in Danubian Domain, as in Fig. 3.
Hateg area (HT) is part of the Hateg-Strei Basin. Hateg basin cluster, were
developed North of Hateg-Sarmisegetusa Regia Fault a strike slip fault with an
orientation NE to SW, one of the major fault which lead to basin forming. In the
area took place two seismic sequences one from March 2011 with 19 earthquakes
and second from September 2013 with 31 earthquakes, The highest magnitude is
M
w
= 4.3, 8 September 2013 [16, 17].
Resita-Moldova Noua area is situated along Oravita-Moldova Noua Fault.
This fault is a master fault of the Alpine tectonic processes in the area, being the
fault through the Supragetic nappe covers the Getic nappes and where the seismic
sequence from April–August 2002 took place, with a total of 70 earthquakes, the
maximum magnitude being 4.1 (M
w
) for the earthquake of August 4, 2002 [18].
Teregova area, is situated at the intersection of two faults, one with a north-south
orientation and another one with a west-east orientation near the thrust of Getic Nappe
over the Danubian Domain, where seismic sequence from October–November 2014
was generated, with a total of 51 earthquakes. The maximum magnitude observed was
4.1 (M
w
) for the earthquake that occurred on October 31, 2014 [16].
Baile Herculane-Mehadia area is located along the Cerna-Jiu fault (known as
Cerna Graben), right lateral strike slip fault. The maximum magnitude observed
was 5.5 (M
w
) for the earthquake on July 18, 1991.

5 Main active faults from Romania. Part III Article no. 710
Fig. 3 – Seismicity map for 1990–2018 period. After [17].
For the seismicity study, 1648 seismic events were selected from the Romplus
catalogue recorded in 1990–2018 (Fig. 3). The hypocenters of the selected seismic
events are located at depths which do not exceed 51 km. Most of the seismic
activity in the area is focused in the first 20 km of the crust [17].
4. METHODOLOGY
Active faults can be described using different parameters, as those proposed
in [1, 2]. Different authors such as [2, 3] distinguished three main categories of
Seismogenic Sources: Individual Seismogenic Sources described in [11, 12] for
Romania and Seismogenic areas and Macroseismic sources. Our study is providing
geometrical and seismological parameters for the active faults, using only the first
two categories of seismogenic sources.
Individual Seismogenic Sources (ISS) are defined by geological and geophysical
data and are characterized by a full set of geometric (strike, dip, length, width and
depth), kinematic (rake), and seismological parameters (single event displacement,
magnitude, slip rate).
Every parameter of each Individual Seismogenic Source is qualified according
to the type of analysis that was done to determine it. The qualifiers are defined as
follows [2, 3]:

Article no. 710 M. Diaconescu et al. 6
– Literature Data (LD): data taken from a published source.
– Original Data (OD): original data obtained in field surveys, unpublished
original measurements and interpretations for the purposes of this Database;
– Expert Judgement (EJ): assignments made by the compiler on the basis of
tectonic information or established knowledge at a larger scale than that of the
seismogenic source distribution under consideration and data collected from
studies published in scientific journals and technical reports of research projects.
We use 93 earthquakes (Fig. 4) with fault plane solutions in terms of nodal
planes to describe the faults from a seismological point of view. The fault plane
solutions have been obtained as in [11], from [14, 18, 19].
Fig. 4 – Earthquakes with fault plane solutions.
The earthquakes catalogue
used is the Romplus catalogue [20] and a local
catalog with earthquakes from south-west Romania [19].
5. RESULTS AND CONCLUSIONS
Regarding the parameterization of the faults, this is done in the form of a
table in SHARE/DISS manner. We attach the parameterization of the: Hateg-

7 Main active faults from Romania. Part III Article no. 710
Sarmisegetusa Regia Fault (Table 1), Moldova Noua – Oravita Fault (Table 2),
Cerna-Jiu Fault (Table 3) and the Western Teregova Fault (Table 4).
Table 1
Hateg-Sarmisegetusa Regia Fault
Total lenght (km) 17 km EJ Inferred from regional tectonic
Active length (km) 17 OD Inferred from earthquakes distribution
Wide (km) 2 km OD Inferred from earthquakes distribution
Minimum depth (km) 1.5 km OD Inferred from earthquakes distribution
Maximum depth (km) 10 OD Inferred from earthquakes distribution
Strike (degree) N
0
157 E
0
OD Based on fault plane solution
Dip(degree) dip 70
0
OD Based on fault plane solution
Rake(degree) /
Slip(m) –4
0
/ 0.0378m OD
Based on fault plane solution /
Calculated from M
o
using the
relationship from [21]
Max magnitude M
w
= 4 (08.09.2013) LD Based on [14]
Hateg-Sarmisegetusa Regia Fault (Table 1) is a NE-SW oriented fault wich
play a principal role in basin fomation. Throughout such system of fractures, as
Hateg-Sarmisegetusa Regia Fault, basin formed by dipping some of the basement
blocks with fault plane dipping to the south east and a NE-SW orientation. The
Hateg–Strei basin could be assimilated as a composite seismic source as in [2]. The
predominant type faulting, strike slip, is replaced by normal faults, on the NE side
of the zone and reverse faults, on the SE side of the zone. In the E part of the area,
the type of faults is undefined, suggesting the existence of a heterogeneous
structure, fractured following the variable reactivation of tectonic regimes [14, 16].
Moldova Noua-Oravita fault (Table 2) is master fault of the Resita-Moldova
Noua composite sesimic source, this fault that has an important role of the Alpine
tectonic processes in the area, being the fault through the Supragetic nappe covers
the Getic nappes and where the seismic sequence from April–August 2002 was
generated [18].
Table 2
Moldova Noua-Oravita Fault
Lungime totala (km) 75 km EJ Inferred from regional tectonic
Active length (km) 45 OD Inferred from earthquakes distribution
Wide (km) 7 km OD Inferred from earthquakes distribution
Minimum depth (km) 3 km OD Inferred from earthquakes distribution
Maximum depth (km) 18 km OD Inferred from earthquakes distribution
Strike (degree) N 9
0
E
LD Based on [18]
Dip(degree) dip 65
0
LD Based on [18]
Rake(degree) / Slip(m) 145
0
/ 0.033 LD/
ER
Based on [18] / Calculated from M
o
using the relationship from [21]
Max magnitude M
w
= 4.1 (02.08.2002) LD Based on [18]

Article no. 710 M. Diaconescu et al. 8
Table 3
Cerna-Jiu Fault
Total lenght (km) 46 km EJ Inferred from regional tectonic
Active length (km) 46 OD Inferred from earthquakes distribution
Wide (km) 10 km OD Inferred from earthquakes distribution
Minimum depth (km) 2 km OD Inferred from earthquakes distribution
Maximum depth (km) 20 km OD Inferred from earthquakes distribution
Strike (degree) N 23
0
E
LD Based on fault plane solution
Dip(degree) 47
0
LD Based on fault plane solution
Rake(degree) / Slip(m) 178
0
/ 0.214 LD/
ER
Based on fault plane solution /
Calculated from M
o
using the
relationship from [21]
Max magnitude M
w
= 5.7 (18.07.1991) LD Based on [14]
Seismicity in the region concentrates along the contact between the South
Carpathians Orogen and Getic Depression, especially along the Cerna-Jiu Fault
(Table 4) and in the Neogene Intra-Carpathian Depressions. like Orsova-Baile
Herculane-Mehadia area. Cerna-Jiu fault, vertical fault with a NNE-SSW orientation,
play a master role in Alpine evolution of the area and in neogen-Quaternary
subsidence, along this fault taking place movements of tectonic units from eastern
part of the Danubian Domain [14, 18, 22] .
The focal mechanisms in Caransebes-Teregova Area are compatible with the
large-scale transcurrent deformation recorded during the Tertiary drift of the ALCAPA
and Tisza-Dacia units into the Carpathians embayment by the rapid roll-back of a
slab attached to the European continent [14].
Table 4
West Teregova Fault
Total length (km) 40 km EJ Inferred from regional tectonic
Active length (km) 15 OD Inferred from earthquakes distribution
Wide (km) 3 km OD Inferred from earthquakes distribution
Minimum depth (km) 2 km OD Inferred from earthquakes distribution
Maximum depth (km) 17 km OD Based on fault plane solution
Strike (degree) N 14
0
E
LD Based on fault plane solution
Dip(degree) dip 76
0
LD Based on fault plane solution
Rake(degree) / Slip(m) 158
0
/ 0.0318 m LD/
ER
Based on fault plane solution /
Calculated from M
o
using the
relationship from [21]
Max magnitude M
w
= 4.1 (31.10.2014) LD Based on [14]
This was contemporary with the formation at the interior of the Carpathians
of a number of well-studied transtensional to pull-apart basins, such as Haţeg and
Caransebes-Teregova (Table 4) and Orsova Baile Herculane-Mehadia basins. The
largest amount of transcurrent deformation took place during the right-lateral

9 Main active faults from Romania. Part III Article no. 710
movement of the South Carpathians in respect to the stable Moesian unit. The
clockwise rotation and N- to E-ward movement of the upper Carpathians units in
respect to Moesia, were accommodated trough significant amounts of dextral
strike-slip deformations. The fault plane solutions follow closely this pattern and
the nodal planes oriented NE-SW in Caransebes-Teregova area having a right-
lateral movements. These are mainly thrusts which delinate WNW verging nappes
inside Median and Marginal Dacides, such as Sichevita-Retezat thrust [14, 16].
The relatively high stress drop values are compatible with a stress regime
specific for intra-continental tectonics [16].
Acknowledgements. This work was supported by the Project Nucleu 2016-2017 (PN 16 35 01 12) –
CREATOR, Nucleu 2018 (PN18150101)-CIRRUS and NUCLEU 2019 (PN19 08 01 02).
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