Petra Stepancikova | Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic (original) (raw)

Papers by Petra Stepancikova

Geografie. Sborník České geografické společnosti, 2003

epa n c i k 0 va: River Terraces at the lower course of the Scizava River from VrabC5i Brod to Ka... more epa n c i k 0 va: River Terraces at the lower course of the Scizava River from VrabC5i Brod to Kamenny PNvoz.-Geografie-Sbornik CGS, 108,3, pp. 216-226 (2003).-A detailed geomorphological analysis of terraces within this part of the valley is submitted in the article. Only denudated relics of these terraces occur in the studied section of the valley. Comparison to the terrace system of the Vltava River was exerted for the arrangement ofthe Sazava terraces into the stratigraphical chronology. The terraces of the groups IlIA (Gunz 2) up to VII (Wurm) have been identified in the examined part of the Sazava valley. KEY WORDS: geomorphology-river terraces-valley-Bohemian massif-Central Bohemian Hilly land.

Journal of Applied Geophysics, May 1, 2011

This paper presents the results of two separate geophysical investigations undertaken across the ... more This paper presents the results of two separate geophysical investigations undertaken across the Sudetic Marginal Fault zone in the Bohemian Massif. This fault zone represents one of the most important tectonic features in central Europe. The first, preliminary, investigation used electrical resistivity tomography (ERT) to define the exact position of the main fault at two localities (Kamenička &amp;amp;amp;amp;amp;amp;amp; Bílá Voda).

Palaeogeography, Palaeoclimatology, Palaeoecology, 2022

Quaternary International, Aug 1, 2023

AGU Fall Meeting Abstracts, Dec 1, 2018

$Research paper thumbnail of Pleistocene speleothem fracturing in the foreland of the Western Carpathians: a case study from the seismically active eastern margin of the Bohemian Massif$

Geological Quarterly, Mar 25, 2015

We stud ied speleothem-frac tur ing styles and their tec tonic con text in three cave sys tems si... more We stud ied speleothem-frac tur ing styles and their tec tonic con text in three cave sys tems sit u ated in the east ern Bo he mian Mas sif, close to the West ern Carpathians orogenic front: the Za hájovnou, Javoříčko, and Mladeč caves. The mor phol ogy of the speleothems in par tic u larly thin sta lac tites, and sup port ing ev i dence from the cave in te rior, in di cates a tec tonic or i gin of the break age. U/Th se ries dat ing of the sta lac tites, sup ported by Op ti cally Stim u lated Luminiscence (OSL) and 14 C dat ing of soft sed i ments in di cate that most of the frac tur ing oc curred in the Up per Pleis to cene, with the last frac tur ing events cor respond ing to MIS6 and MIS5 stages. OSL dat ing of faulted soft-sed i ment infill may even in di cate that lat est Pleis to cene to Early Ho lo cene tec tonic events oc curred in the Mladeč Cave. The speleothem frac tur ing is dis cussed in the re gional con text of the seis mi cally ac tive Nysa-Morava Zone sit u ated at the junc tion be tween the Bo he mian Mas sif (Elbe Fault Zone) and the West ern Carpathians. This study pro vides the first ev i dence of palaeoseismicity from the subsurface and the old est dated palaeoseismicity from the con tact be tween the West ern Carpathians and the Bo he mian Mas sif.

Quaternary International, Sep 1, 2017

Abstract Successions of colluvia and loesses covering the faults in the eastern and central parts... more Abstract Successions of colluvia and loesses covering the faults in the eastern and central parts of the Bohemian Massif were exposed in six trenches (two trenches at each fault, up to 6 m deep) and studied in detail in terms of stratigraphy and deformation. Based on OSL and radiocarbon ages these sediments were dated as Weichselian Early Glacial to Younger Dryas/Holocene (∼120 ka to 11 ka). On the Kosiř fault (NW-SE strike), the offset strata bring evidence for Late Pleistocene oblique slip (normal and strike-slip components) on the main fault plane with minimum slip rate in order of 0.1 mm/a. Although the undisrupted topsoil suggests the absence of significant slip in Holocene and no clear evidence of paleoseismic events was found, this fault structure should be included in seismic hazard assessment. Conversely, on the Hluboka and Diendorf-Boskovice faults (NW-SE and NNE-SSW strikes, respectively), the tectonic slip is contradicted for the last 15–23 ka based on dating of undeformed strata sealing the fault planes. Multiple independent evidence suggests that these two faults were not active in Late Pleistocene at least and their prominent scarps is probably largely due to exhumation by differential denudation. Examples given document the mechanisms of slope-related deformations which may lead to destruction of the records of older faulting and occasionally produce deformation structures resembling the tectonic ones.

Geomorphology, Feb 1, 2019

Offset alluvial fans along the Elsinore fault in the south-central Coyote Mountains were studied ... more Offset alluvial fans along the Elsinore fault in the south-central Coyote Mountains were studied to resolve an average late Quaternary slip rate for this major western strand of the San Andreas fault system in southern California. Alluvial fans and their offsets were mapped using high-resolution DEMs combined with field observations of fan-surface morphology and the character of the soils developed in each fan remnant. Clast assemblage data was used to determine the source of each alluvial fan upstream of the fault, and U-series dating of pedogenic carbonate was used to estimate minimum ages of the alluvial fan surfaces. Forty U-Th dates on pedogenic carbonate confirm the utility of the technique for dating late Pleistocene alluvium in arid regions and suggest that age variation among late Pleistocene fans grouped on the basis of soils and geomorphic criteria may be significant. Based on these data, the southernmost segment of the Elsinore fault has sustained a slip rate of 2.4 ± 0.4 mm/y for the past 60-70 ka and probably for the past 150 ka. Because displacement in the most recent surface rupture increases northwest of our slip rate sites, this rate is likely a minimum for the southern Elsinore fault, with the actual rate more likely close to 3 mm/y in the central part of the range. These new data confirm that slip gradients along individual fault segments must be considered when estimating pre-Holocene slip rates for seismic hazard estimates. These new results show that the southern Elsinore fault accounts for about 6% of the total relative motion between North America and the Pacific lithospheric plates in southernmost California. Assessment of previous estimates of slip in the most recent event suggests earthquakes of about Mw 6.8 and, when combined with the slip rate data, a recurrence of such events about every thousand years.

Geophysical Journal International, May 8, 2020

SUMMARYWe present results from complementary geological, topographic, seismic and electrical resi... more SUMMARYWe present results from complementary geological, topographic, seismic and electrical resistivity surveys at the Sagebrush Flat (SGB) site along the Clark fault (CF) strand of the San Jacinto fault zone trifurcation area southeast of Anza, California. Joint interpretation of these data sets, each with unique spatiotemporal sensitivities, allow us to better characterize the shallow (<100 m) fault zone at this structurally complex site. Geological mapping at the surface shows the CF has three main subparallel strands within a <100 m zone with varying degrees of rock damage. These strands intersect units of banded gneiss and tonalite, and various sedimentary units. Near the surface, the weathered but more intact tonalite and gneiss to the southwest have relatively high VP. The low-lying flat sedimentary basins around the two southwestern-most CF strands and elevated damaged gneiss to the northeast have lowest VP <500 m s–1. The high relief of the northeast gneiss unit may in part be explained by its extensive damage and inferred increased relative rock uplift. Resistivity imaging shows the unconsolidated dry basin sediments (maximum >1300 Ohm.m) contrasted against the compacted fine-grained (potentially wet) materials within the CF core and the Bautista Formation (minimum <40 Ohm.m), which is slightly elevated above the flat basins. The inverse relationship between VP (increases) and resistivity (decreases) in the uppermost ∼15 m can be characterized as log–log linear with slopes of –2.6 to –4. At depths >30 m, the velocity heterogeneity near the surface merges into larger-scale structures that are generally slower on the northeast side of the CF core compared to the southwest side (as much as ∼40 per cent reduction in average VP). A previous study revealed a 20–37 per cent variability in peak ground velocities across the SGB site from local earthquakes. The upper end of that range is associated with the near-surface unconsolidated sedimentary basins and northeast damaged gneiss unit. Preliminary analysis of time-dependent topography mostly shows effects of changing vegetation and anthropogenic activity.

International Journal of Earth Sciences, Dec 11, 2014

We give an interpretive review of the geological evolution of the Nysa-Morava Zone (NMZ)-a Late C... more We give an interpretive review of the geological evolution of the Nysa-Morava Zone (NMZ)-a Late Cenozoic tectonically active region of the NE Bohemian Massif located at its contact with the Western Carpathians' orogenic front. This crustal domain, delimited by generally NW-SE-striking fault system, is characterised by Oligo-Miocene and Plio-Pleistocene volcanic activity, regionally anomalous, weak historical and present-day seismicity and increased CO 2 flux. The NMZ hosts several elongated, mostly NW-SE-trending, graben-like sedimentary basins (Upper Morava Basin System), which are filled by more than 300-m-thick succession of clastic fluvial/lacustrine sediments of Pliocene-Quaternary age. Based on geometric relations, basin architecture, coincidence of seismicity with CO 2 escape and sparse focal mechanism data, a model is proposed, which explains this active domain as a transfer zone developed between major WNW-ESE and NW-SE faults in a right-lateral transpressional setting. It is suggested that slow horizontal slip at these faults resulted in local permutations of the largest and medium stress directions and formation of transtensional crustal domains in the NMZ. Moreover, relation of the NMZ to the Alpine-Carpathian system and sedimentary grabens in its foreland is

Tectonics, Mar 13, 2012

The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural labora... more The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural laboratory for studies of postorogenic landscape evolution. This work reveals both the exhumation history of the region and the paleoactivity along the Sudetic Marginal Fault (SMF) using zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th)/ He (AHe) dating of crystalline basement and postorogenic sedimentary samples. Most significantly, and in direct contradiction of traditional paleogeographic reconstructions, this work has found evidence of a large Cretaceous sea and regional burial (to >6.5 km) of the Carboniferous-Permian basement in the Late Cretaceous ($95-80 Ma). During the burial by sediments of the Bohemian Cretaceous Basin System, the SMF acted as a normal fault as documented by offset ZHe ages across the fault. At 85-70 Ma, the basin was inverted, Cretaceous strata eroded, and basement blocks were exhumed to the near surface at a rate of 300m/MaasevidencedbyLateCretaceous−PaleoceneAFTagesandthermalmodelingresults.ThereisnoappreciabledifferenceinAFTandAHeagesacrossthefault,suggestingthattheSMFactedasareversefaultduringexhumation.InthelateEocene−Oligocene,thebasementwaslocallyheatedto<70°CbymagmaticactivityrelatedtoopeningoftheEgerriftsystem.Neogeneoryoungerthermalactivitywasnotrecordedinthethermochronologicaldata,confirmingthatlateCenozoicupliftanderosionofthebasementblockswaslimitedtolessthan300 m/Ma as evidenced by Late Cretaceous-Paleocene AFT ages and thermal modeling results. There is no appreciable difference in AFT and AHe ages across the fault, suggesting that the SMF acted as a reverse fault during exhumation. In the late Eocene-Oligocene, the basement was locally heated to <70°C by magmatic activity related to opening of the Eger rift system. Neogene or younger thermal activity was not recorded in the thermochronological data, confirming that late Cenozoic uplift and erosion of the basement blocks was limited to less than 300m/MaasevidencedbyLateCretaceous−PaleoceneAFTagesandthermalmodelingresults.ThereisnoappreciabledifferenceinAFTandAHeagesacrossthefault,suggestingthattheSMFactedasareversefaultduringexhumation.InthelateEocene−Oligocene,thebasementwaslocallyheatedto<70°CbymagmaticactivityrelatedtoopeningoftheEgerriftsystem.Neogeneoryoungerthermalactivitywasnotrecordedinthethermochronologicaldata,confirmingthatlateCenozoicupliftanderosionofthebasementblockswaslimitedtolessthan1.5 km in the study area.

Studia Geophysica Et Geodaetica, Jun 8, 2018

The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW... more The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW-NE trending Ohře/Eger Graben and the NNW-SSE trending Mariánské Lázně Fault, which has been reactivated several times in the geological history and controlled the formation of the Tertiary Cheb Basin. The broader area of the Cheb Basin is also related to permanent seismic activity of M L 3+ earthquake swarms. The Eastern Marginal Fault of the Cheb Basin (northern segment of the Mariánské Lázně Fault) separates the basin sediments and underlying granites in the SW from the Krušné Hory/Erzgebirge Mts. crystalline unit in the NE. We describe a detailed geophysical survey targeted to locating the Eastern Marginal Fault and determining its geometry in the depth. The survey was conducted at the Kopanina site near the Nový Kostel focal zone, which shows the strongest seismic activity of the whole Western Bohemia earthquake swarm region. Complex geophysical survey included gravimetry, electrical resistivity tomography, audiomagnetotellurics and seismic refraction. We found that the rocks within the Eastern Marginal Fault show low resistivity, low seismic velocity and density, which indicates their deep fracturing, weathering and higher water content. The dip of the fault in shallow depths is about 60 towards SW. At greater depths, the slope turns to subvertical with dip angle of about 80. Results of geoelectrical methods show blocky fabric of the Cheb Basin and deep weathering of the granite bedrock, which is consistent with geologic models based on borehole surveys.

Bulletin of the Seismological Society of America, Oct 20, 2015

ABSTRACT

Tectonics, Jun 1, 2023

The Trans‐Mexican Volcanic Belt is an active continental volcanic arc related to subduction along... more The Trans‐Mexican Volcanic Belt is an active continental volcanic arc related to subduction along the Middle America trench. It is characterized by intra‐arc extension resulting into several major arc‐parallel active fault systems and tectonic basins. The Acambay graben, one of the largest of these basins, is located near Mexico City, in the central part of this province. In 1912, a M 6.9 earthquake ruptured the surface along the northern border of the graben together with at least two other faults. In this paper, we analyze the paleoseismic history of the southern border of the Acambay Graben, with new observations made in one natural outcrop and four paleoseismological trenches excavated across branches of the Venta de Bravo Fault at the site where it overlaps with the Pastores Fault. We present evidence of at least two paleo‐earthquakes that occurred between 12,190 ± 175 and 5,822 ± 87 cal year BP and between 647 ± 77 and 250 cal year BP. On one of these branches, we estimate a minimum slip‐rate value between 0.1 and 0.23 mm/year for the last 12 ka and a mean recurrence interval of 8.5 ± 3 ka. By considering several likely rupture lengths along the Venta de Bravo and Pastores faults, we calculated a maximum possible magnitude of Mw 7.01 ± 0.27. Finally, by correlating events recorded along different faults within the Acambay Graben, we discuss several possible rupture coalescent scenarios and related consequences for Mexico City.

Preliminary results of trenching study for late Quaternary slip assessment of the Kosiř fault are... more Preliminary results of trenching study for late Quaternary slip assessment of the Kosiř fault are given. Other selected examples illustrate the slope-related deformations on fault scarps leading to destruction of the records of older faulting and occasionally producing deformation structures resembling the tectonic ones.

EGU General Assembly Conference Abstracts, Apr 1, 2017

EGU General Assembly Conference Abstracts, Apr 1, 2012

* V ramci projektu byl detailně vymapovan hlubocký zlom v useku Munice-Vrato, kde ma zjevne geolo... more * V ramci projektu byl detailně vymapovan hlubocký zlom v useku Munice-Vrato, kde ma zjevne geologicke, geofyzikalni a geomorfologicke projevy. Takto indikovaný zlom lze z hlediska možne reaktivace považovat za samostatnou strukturu, jejiž hypoteticke pokracovani dale sz. a jv. směrem je výrazně poruseno systemy zlomů s.-j. až ssv.-jjz. směru. Delka takto indikovaneho zlomu je pouze 13 km. Velke množstvi indicii a důkazů ukazuje, že hlubocký zlom je neaktivni a jeho morfologicke projevy jsou v prve řadě výsledkem diferencialni eroze na styku velmi slabě zpevněných sedimentů panevni výplně a odolných hornin krystalinika. Ve středni casti zlomu byla intenzita eroze výrazně zvýsena rychlým zahlubovanim Vltavy. Výzkum hlubockeho zlomu neprokazal žadne paleoseismicke udalosti v geologickem zaznamu, ani jejich indikace. Výzkum neodhalil žadne nove skutecnosti, ktere by vyžadovaly revizi odhadu seismickeho ohroženi ve studovane oblasti