Source of Analytical Data on Main Faults and Faulted Areas with Seismic Potential
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dbz:diendorf-boskovice_fault [2020/05/29 15:56] petrs |
dbz:diendorf-boskovice_fault [2021/04/29 15:46] petrs [Quaternary] |
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* Results of some long-term geodetic measurements in the region were interpreted as tectonic deformation in several studies (Pospíšil et al. 2009, 2010, 2012; Roštínský et al. 2013). However, editor of this text is skeptical to interpretation of these observations as due to tectonic strain because: | * Results of some long-term geodetic measurements in the region were interpreted as tectonic deformation in several studies (Pospíšil et al. 2009, 2010, 2012; Roštínský et al. 2013). However, editor of this text is skeptical to interpretation of these observations as due to tectonic strain because: | ||
- | - the reported strain rates are too large (10< | + | - the reported strain |
- the locally observed geological records rule out that such deformation at BF could have been operative on a long-term scale during Quaternary; | - the locally observed geological records rule out that such deformation at BF could have been operative on a long-term scale during Quaternary; | ||
- | - the non-tectonic deformation (climatic/ | + | - the non-tectonic deformation (climatic/ |
:!: **Basing on this local evidence the fault activity is currently evaluated in a following way:** | :!: **Basing on this local evidence the fault activity is currently evaluated in a following way:** | ||
*In the southern part of DBF, the sections DF_1 to BF_2 are ranked **class 3**, i.e. assumed or admitted to be active but without direct evidence. Quaternary slip rate at fault sections north of DF_3 is assumed very low (<0.01 mm/y). Southern sections may later be ranked class 1 (demonstrably active) when new earthquake data (better location, focal mechanism) bring clear evidence. | *In the southern part of DBF, the sections DF_1 to BF_2 are ranked **class 3**, i.e. assumed or admitted to be active but without direct evidence. Quaternary slip rate at fault sections north of DF_3 is assumed very low (<0.01 mm/y). Southern sections may later be ranked class 1 (demonstrably active) when new earthquake data (better location, focal mechanism) bring clear evidence. | ||
*In the northern part of DBF, the sections BF_3 to BF_ 17 are ranked **class 4**, i.e. assumed or demonstrated to be inactive. | *In the northern part of DBF, the sections BF_3 to BF_ 17 are ranked **class 4**, i.e. assumed or demonstrated to be inactive. | ||
- | On a theoretical basis, the evaluation of similarly oriented | + | On a theoretical basis, the evaluation of similarly oriented sections |
-expected northward decrease of rate of stress build-up (and hence crustal strain rate), and | -expected northward decrease of rate of stress build-up (and hence crustal strain rate), and | ||
-expected northward decrease of slip potential due to rotation of stress orientation near junction of the Alpine and the West-European stress domains. | -expected northward decrease of slip potential due to rotation of stress orientation near junction of the Alpine and the West-European stress domains. | ||
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<WRAP GROUP> | <WRAP GROUP> | ||
<WRAP column 60%> | <WRAP column 60%> | ||
- | *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 | + | *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 |
- | *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 morpholineaments | + | *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 |
- | *Also note the N-S oriented | + | *Also note the N-S oriented |
</ | </ | ||
<WRAP column 30%> | <WRAP column 30%> | ||
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*The 7 m thick sediment succession includes (from bottom to top; see photo an scheme below left): sandy eluvium, coarse gravels (partly cemented), silty clays with angular detritus, layer of colluvium, fine loams with paleosol, and loess loams to loess with interlayer of laminated or cross bedded fine sands. While the layers no. 6 and 7 (see figure) give OSL ages within the span of 36-63 ka, dating of the deeper strata remains problematic. Ages largely exceeding 100 ka are very likely and Tertiary age is not ruled out (Prachař 2017). | *The 7 m thick sediment succession includes (from bottom to top; see photo an scheme below left): sandy eluvium, coarse gravels (partly cemented), silty clays with angular detritus, layer of colluvium, fine loams with paleosol, and loess loams to loess with interlayer of laminated or cross bedded fine sands. While the layers no. 6 and 7 (see figure) give OSL ages within the span of 36-63 ka, dating of the deeper strata remains problematic. Ages largely exceeding 100 ka are very likely and Tertiary age is not ruled out (Prachař 2017). | ||
*Clay-filled fault within the shear zone contains slickenside (dipping 66° to NW) with 2 sets of slickenlines, | *Clay-filled fault within the shear zone contains slickenside (dipping 66° to NW) with 2 sets of slickenlines, | ||
- | *Thin blind sand dike cuts through the lower part of the sedimentary sequence above the fault. The dike connetcs | + | *Thin blind sand dike cuts through the lower part of the sedimentary sequence above the fault. The dike connects |
*This clastic dike is interpreted as an effect of local liquefaction generated by earthquake-induced shaking. Its location above the observed fault is likely an effect of stress concentration within loose and water-saturated deposit above the breakpoint in bedrock topography and lithology (structurally controlled failure of gravitationally unstable sediment) | *This clastic dike is interpreted as an effect of local liquefaction generated by earthquake-induced shaking. Its location above the observed fault is likely an effect of stress concentration within loose and water-saturated deposit above the breakpoint in bedrock topography and lithology (structurally controlled failure of gravitationally unstable sediment) | ||
*Although the inferred hypothetical earthquake is not necessarily related to Diendorf fault, it is recommended to be assumed related for purpose of SHA (Špaček et. al. 2018). | *Although the inferred hypothetical earthquake is not necessarily related to Diendorf fault, it is recommended to be assumed related for purpose of SHA (Špaček et. al. 2018). | ||
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*Trench HOS-1 (25 m long and 4 m deep; WGS84: 48.9476°N, 16.2726°E) with fault in Lower Miocene sediments sealed by Late Pleistocene sands and loess loam. Špaček et al. (2017, 2018)\\ | *Trench HOS-1 (25 m long and 4 m deep; WGS84: 48.9476°N, 16.2726°E) with fault in Lower Miocene sediments sealed by Late Pleistocene sands and loess loam. Špaček et al. (2017, 2018)\\ | ||
- | *Strong imbrication, | + | *Strong imbrication, |
*Deformed Neogene sediments are unconformably overlain by Pleistocene strata. The irregular, up to 30 cm thick basal layer of sands and gravelly sands with mostly angular clasts of local provenance has a sharp base and the luminescence dating of a single sample gives the age of 16-18 ka. Locally, at the base of Quaternary a thin sub-horizontal layer of parallel-laminated sand is developed and partly incorporated in coherently bended or apparently undeformed parts of Miocene sand. Luminescence age of a single sample from this layer is 20-24 ka. | *Deformed Neogene sediments are unconformably overlain by Pleistocene strata. The irregular, up to 30 cm thick basal layer of sands and gravelly sands with mostly angular clasts of local provenance has a sharp base and the luminescence dating of a single sample gives the age of 16-18 ka. Locally, at the base of Quaternary a thin sub-horizontal layer of parallel-laminated sand is developed and partly incorporated in coherently bended or apparently undeformed parts of Miocene sand. Luminescence age of a single sample from this layer is 20-24 ka. | ||
*The above described sediments are overlain by 1-1.8 m thick layer of loess loam which is mixed with sands at the base. Its luminescence age is 26-29 ka. This age inversion (if real) suggests the emplacement of the loess loam without resetting of the luminescence signal (e.g. in a form of mudflows derived from older loess). Apparent age inversion due to dating errors can not be ruled out, however. | *The above described sediments are overlain by 1-1.8 m thick layer of loess loam which is mixed with sands at the base. Its luminescence age is 26-29 ka. This age inversion (if real) suggests the emplacement of the loess loam without resetting of the luminescence signal (e.g. in a form of mudflows derived from older loess). Apparent age inversion due to dating errors can not be ruled out, however. | ||
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**editor:** [[spacek@ipe.muni.cz|Petr Špaček]] | **editor:** [[spacek@ipe.muni.cz|Petr Špaček]] | ||
- | *Refraction and reflection seismic profile crossing the fault line (Alexa 2017; diploma thesis supervised by J. Valenta) showing a >50 m vertical offset at the base of low-velocity strata (assumed Lower Miocene sediment and/or strongly weathered crystalline) and a >40 m thick, apparently vertically undisplaced, | + | *Refraction and reflection seismic profile crossing the fault line (Alexa 2017; diploma thesis supervised by J. Valenta) showing a >50 m vertical offset at the base of low-velocity strata (assumed Lower Miocene sediment and/or strongly weathered crystalline) and a >40 m thick, apparently vertically undisplaced, |
<WRAP GROUP> | <WRAP GROUP> | ||
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===== Other notes===== | ===== Other notes===== | ||
- | **Ongoing | + | **Ongoing |
*EM conductivity mapping of fault and covering sediments south of Hostěradice (Fojt and Špaček, ongoing), near Ivančice, Lesonice and Bořitov (planned) | *EM conductivity mapping of fault and covering sediments south of Hostěradice (Fojt and Špaček, ongoing), near Ivančice, Lesonice and Bořitov (planned) | ||
*studies on cross structures | *studies on cross structures |