Table of Contents


Diendorf - Boskovice fault system

Structure ID: DBF
Fault Section IDs: DF_1-10; BF_1-17; WEI_1-3
Related terms: Diendorf fault (ger: Diendorfer Störung), Boskovice Graben fault (cze: okrajový zlom boskovické brázdy), Weitzendorf fault (ger: Weitzendorfer Störung; cze: weitzendorfský zlom)

Editor: Petr Špaček
First published: Aug 2019 | Last update: 29. 5. 2024

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General description

Diendorf-Boskovice fault system (DBF) is more than 200 km long fault structure running in the general NE-SW direction from the Alpine thrust front in Austria to the transverse faults of the Haná fault zone in the Czech Republic. It is formed by two major faults: the Diendorf fault (DF) to the south and the eastern marginal fault of the Boskovice half-graben, here termed the Boskovice Graben fault (BF), to the north (Fig. 1). Physical linking of both faults in the flat area of the Alpine molasse/Carpathian foredeep basins is strongly supported by geophysical data (see Špaček at el. 2018). Here, the formal border between DF and BF is located in the external part of the Carpathian foredeep basin. Southwestward continuation of DF beneath the Alpine nappes is unclear. To the north-northeast the BF is terminated by cross-cutting faults with apparently younger slip (the Haná Fault Zone). The parallel Weitzendorf fault and some minor faults (not necessarily included in the database) are formally assigned to DBF.


Fault structure and dip

At shallow levels the fault is always steep, dipping either due W or E or vertical in both BF and DF. At general scale the BF is expected to be steeply inclined to WNW. The azimuth of the fault trace ranges between <20° and >45°.

The fault core, where observed, is often built by several meter wide mélange with fragments or bodies of limestones and greywackes (sections BF_2 through BF_14; Špaček et al. 2002) locally containing dark coloured clays. Surface observations near Zöbing (vineyards north of Kammern) suggest that the strongly deformed zone may be >10 m broad there. Similar width is expected elsewhere in Permian and crystalline rocks. In trench near Hostěradice, a 5-6 m wide zone of strong shearing and additional >5 m wide damage zone with dense small-scale faults is exposed in Lower Miocene clays and sands. The former contains frequent small fragments of weathered crystalline rocks.

A <20 to 250 m wide damage zone of the main fault is documented in Early Miocene sediments across a large part of BF_1 section by EM conductivity mapping (Fojt and Špaček, unpublished) and by observations in aerial photographs.

Parallel fault sections (splays of primary fault) are indicated by geological mapping and relief morphology in some parts of DF and BF, in a zone up to 800 m wide. Multiple parallel and oblique faults (observed and assumed) located in a broader zone (within up to 10 km to both sides of the BF and DF) indicate distributed faulting reflecting the complexity of long term evolution in different stress fields.


Cross structures and Segmentation

Cross structures, mostly of general NW-SE strike, traverse the DBF at multiple places, preferentially at its northern, Czech part. These are mainly (from north to south):

  • Fault-bounded Valchov and Blansko „grabens“ (Fig. 1) representing subsided blocks with preserved Upper Cretaceous sediments (e.g. Kettner 1941, Zvejška 1944, Skoršepa and Melichar 2017). These important structures directly disrupt the BF and bring evidence against significant horizontal slip in the northern part of the BF (sections BF_10 through BF_14) after the formation of the depressions in their present-day shape. The sediments of the Blansko depressions are likely disrupted by normal faults collinear with the BF (section BF_11, so called Klemov fault). Relict Miocene sediments are present in both depressions.
  • Minor cross faults of NW-SE to NNW-SSE direction along the whole eastern margin of the Boskovice graben (BF_3 through BF_15) are often drawn in geological maps and mentioned in texts. They are reported to offset the Permian-Carboniferous fill of the basin both at the surface and in coal mines (např. Čepek 1946, Polák 1954, Jaroš 1960, 1961, 1964a, 1972c). However, their position and geometry differ substantially in different maps and hence I assume they are difficult to trace and probably had very small slip in most cases (comp. Jaroš and Malý 2001).
  • Three zones of low relief with relics of Miocene sediments cross the BF in its central and southern parts: The Tišnov-Kuřim zone, the Jihlava river valley near Ivančice and the southern margin of the Boskovice graben. These structures represent either tectonically subsided areas or erosional paleovalleys or combination of both. Post-Early Badenian vertical slip was inferred in the Tišnov-Kuřim fault zone (Fig. 1; currently not included in database) where Early Badenian sediments are juxtaposed to Eggenburgian/Ottnangian ones along a fault of NW-SE strike (Hanžl et al. 2001a). Similarly, at the southern margin of the Boskovice graben (between Rakšice and Lesonice), NW-SE trending faults seem to terminate the relic of Badenian sediment and small-scale slip at one of these cross faults was observed to offset Early Miocene strata in a trench (Prachař et al. 2017a).
  • Lower Miocene and relict Middle Miocene sediments of the Dyje-Svratka Lowland (Fig. 1) cover the fault sections DF_6 through DF_8 and BF_1. These sediments represent marginal facies of Alpine-Carpathian Foredeep. It is likely that the sediments are part of subsided area affected by normal faulting (comp. Dlabač et al. 1969, Dlabač 1976, Prachař 1970a, 1970b, Čtyroký 1982). ERT measurements made at two topolineaments near Hnízdo and Strachotice (Špaček et al. 2016) likely indicate faults with substantial offset of strata. Small scale faults are documented at localities Lechovice and Stošíkovice. However, faults with significant slip have never been observed directly and there is no geophysical indication of clear significant offset in a map. Therefore, only small slip and/or prevailing normal slip component must be assumed.
  • One of the more expressive faults in the Dyje-Svratka Lowland with larger normal slip component has been reported as the Slup fault (Fig. 1; Buday et al. 1963; Kalášek et al. 1963, Batík et al. 1970, 1977, Dornič et al. 1984, 1985a,b; currently not included in the database). It has been drawn in geological maps between Šatov, Hnízdo and Slup, with general N-E strike, crossing the DF_6 section. Its geometry, however, seems to be poorly constrained. Based on drills, relative vertical offset of 100-150 m has been inferred between the southern, subsided block with Karpathian sediments and the northern block with only Eggenburgian-Ottnangian sediments preserved.
  • FIXME Segmentation near Langenlois.
  • South of Melk, near Schönbühel a.d. Donau (Fig. 1), a pronounced scarp of WNW-ESE direction, very likely a fault, crosses the DF. As it is not offset by the DF, it provides evidence against significant strike slip at sections DF_1, 1a and 9.

Schematic map of DBF

Fig.1. Schematic map of DBF with some basic features mentioned in text: Acronyms alphabetically: bb – Boskovice graben, BF – Boskovice graben marginal fault, BG – Blansko graben, DF – Diendorf fault, HFZ – Haná fault zone, mh – Miroslav horst, SCH – scarp near Schönbühel, SF – Slup fault, TZ – Tišnov—Kuřim zone, VG – Valchov graben, WEI – weitzendorf fault.


Scarp morphology

Surface morphology at the fault trace varies significantly, largely due to different degree of differential erosion at contacts of rocks with similar vs. contrasting mechanical properties.


Observed seismicity

This section will be revisited after completion of earthquake catalogue (submitted deliverable of Prachař and Pazdírková for WP1)! It is now based on review in Lenhardt et al. (2007) and preliminary compilations of ZAMG Vienna and IPE Brno (Pazdírková, unpublished) - see Fig. 2.

  • Repeated occurrence of weak earthquakes near the southern part of DF is most noticeable feature along the whole DBF. This cluster of epicentres seems slightly anomalous even on the scale of the southernmost Bohemian Massif. Maximum macroseismic intensities observed for earthquakes near Krems and Melk are I0=5-6° EMS-98 (largest intensity reported earthquake near Senftenberg in 1959). The corresponding estimated maximum magnitude is Mw≈3.5 FIXME.
  • Coverage by seismic stations of this part of Austria has been loose until recently and large location errors in order of several kilometres must be expected for older instrumentally recorded earthquakes. The error of location exceeding 10 km should be considered everywhere for historical earthquakes based on infrequent macroseismic observations. Our knowledge on the earthquake foci spatial distribution is still too poor to allow clear identification of the active structure, however, its association with DF (sections DF_1a, 1 and 2) is not unlikely.
  • Few other known instrumentally or macroseismically recorded earthquakes are scattered along DBF, with magnitude up to ML=2.5 (near Hostěradice, >3 km away from BF_1 and BF_2; years 2000 and 2014) and (I0=4-5° (near Kunštát, <6 km away from BF_11; year 1916).
  • In general, modern seismicity along BF and northern DF is very weak and similar to background seismicity both in terms of rate and magnitude.

Earthquake epicentre map in the vicinity of DBZ.

Fig. 2. Epicentre map of historical earthquakes (period 1700-1989; yellow circles) and instrumentally located earthquakes (after 1989; red circles) in the broader vicinity of DBF (from unpublished preliminary catalogue compiled by J. Pazdírková, 2018).


Pre-Miocene evolution


Fault activity in late Cenozoic

Tertiary

Quaternary

Following evidence is considered in the assessment of Quaternary activity:

:!: Basing on this local evidence the fault activity is currently evaluated in a following way:

On a theoretical basis, the evaluation of similarly oriented sections of DBF by different activity ranks may be justified by:

  1. expected northward decrease of rate of stress build-up (and hence crustal strain rate), and
  2. expected northward decrease of slip potential due to rotation of stress orientation near junction of the Alpine and the West-European stress domains.

(See layer Local evidence in the map. The sites are listed in south-to-north order.)

Schönbühel a.d. Donau: Cross-structure

evi_ID: SCHO_A
fsec_IDs: DF_1, DF_1a, DF_9
editor: Petr Špaček

  • Pronounced scarp of WNW-ESE direction dividing the hilly terrain with narrow valley of Danube to the NE from comparatively flat area with wide Danube valley to the SW. Interrupted and multiple topolineament continues in ESE direction towards Hafnerbach, partly reflecting the structure of the crystalline basement. This scarp, very likely a fault (not identified in geological maps), possibly a minor dip-slip fault once terminating now eroded Tertiary Molasse sediments or thick regolith, seems to lack any horizontal offset by Diendorf fault (sections DF_1, 1a and 9), therefore providing evidence against significant strike slip of the latter after the formation of the former.
  • This structure is likely a part of a system of WNW- to NW- striking faults with small slip amplitude documented by multiple observations and indicated by penetrative presence of topolineaments in an extensive area hosting the whole DF and southern BF. The age of these faults is largely unknown but some of them were observed to displace Quaternary strata. In Dunkelsteiner Wald and Wachau this fault system may host sources of weak seismicity.
  • Also note the N-S oriented topolineaments near Aggasbach Dorf north of here which seem to coincide with deflected valley of Danube river (out of extent of the map shown here).

Relief map of the vicinity of Melk.

Relief map of the vicinity of Melk.



Limberg: Secondary faults. Timing of dip-slip

evi_ID: LIM_A
fsec_ID: DF_4
editor: Petr Špaček


Fault structures in Hengel quarry (Decker 1999).

Structures from Hengel quarry near Limberg. A) Schematic profile and stereodiagram of synsedimentary faults developed in Early Miocene strata in quarry entrance. B) Stereodiagram of sinistral strike-slip faults in the upper floor. Adopted from Decker (1999), Fig. 2.2-5.



Tasovice: Observed sealing strata and inferred paleoearthquake

evi_ID: TAS_A
fsec_ID: DF_7
editor: Petr Špaček Ivan Prachař


Trench RTAS-3 and stratigraphic scheme of exposed sequence of sediments. Trench RTAS-3 and stratigraphic scheme of exposed sequence of sediments covering the faulted bedrock. From Prachař et al. 2017, modified.

Sand dike cutting through the lower part of sedimentary sequence. Sand dike cutting through the lower part of sedimentary sequence. From Prachař et al. 2017, modified.



Lechovice: Cross-structure and inferred paleoearthquake

evi_ID: LECH_A
fsec_ID: BF_1
editor: Petr Špaček

Geological profile in Lechovice road-cut.

Geological profile in Lechovice roadcut. From Špaček et al. (2018), modified.

Detail of sand blow.

Detail of sand blow (structure A in the profile). From Špaček et al. (2018), modified.



Stošíkovice: Cross-structure

evi_ID: STOS_A
fsec_ID: BF_1
editor: Petr Špaček


Structures in Stosikovice sand pit.

Structures in Stošíkovice sand pit. System of small-amplitude NW-striking faults is cut by few younger, E-W striking faults with partly incorporated sandy gravels of assumed Quaternary terrace (Špaček, unpublished).



Hostěradice: Observed sealing strata

evi_ID: HOS_A
fsec_ID: BF_1
editor: Petr Špaček

Hostěradice profile with ERT, interpreted geology and position of the trench. Note vertical exaggeration. From Špaček et al. 2017.

Hostěradice profile with ERT, interpreted geology and position of the trench. Note vertical exaggeration. From Špaček et al. 2017.

Hostěradice trench log. From Špaček et al. 2017.

Hostěradice trench log. From Špaček et al. 2017.



Kadov: Observed sealing strata

evi_ID: KAD_A
fsec_ID: BF_2
editor: Petr Špaček

Profile Kadov

Profile Kadov with ERT, interpreted geology and position of the trench. Note the vertical exaggeration. From Špaček et al. 2017.

Trench Kadov Kadov trench log. From Špaček et al. 2017.



Lesonice: Eroded fault scarp, Timing of last dip-slip

evi_ID: LES_A
fsec_ID: BF_3
editor: Petr Špaček

Seismic profile LES-P1 Stack of SRT and seismic reflection profiles near Lesonice. Modified from Alexa 2017.



Budkovice: Sealing strata

evi_ID: BUD_A
fsec_ID: BF_4
editor: Petr Špaček

Geological profiles near Budkovice Geological profiles across BF near Budkovice. Modified from Špaček et al. (2018).



Main data sources for fault map

Geological maps and explaining texts:

Geophysics:

Other:


Other notes

Ongoing research and possible future work to be done:


References