scholarly journals Morphology and spatio-temporal distribution of lacustrine mass-transport deposits in Wörthersee, Eastern Alps, Austria

2019 ◽  
Vol 500 (1) ◽  
pp. 235-254 ◽  
Author(s):  
Christoph Daxer ◽  
Maddalena Sammartini ◽  
Ariana Molenaar ◽  
Thomas Piechl ◽  
Michael Strasser ◽  
...  
Keyword(s):  
Mass Transport ◽  
Temporal Distribution ◽  
Late Glacial ◽  
Eastern Alps ◽  
Excess Pore Pressure ◽  
European Alps ◽  
Fine Grained ◽  
Spatio Temporal ◽  
Morphological Differences ◽  
Mass Transport Deposits

AbstractIn lakes, landslides can be studied in high resolution due to their accessibility and limited size. Here, we investigate mass-transport deposits in glacigenic Wörthersee (Eastern European Alps) by integration of seismic, sediment core and multibeam bathymetric data. Two outstanding landslide events were revealed: the first occurred in the Late Glacial, leading to multiple deposits of up to 15 m thickness; they consist of sandy turbidites and mudclast conglomerates, which are overlain by a 2.5 m thick megaturbidite. The extensive, likely earthquake-triggered failure linked to this event was preconditioned by rapid sedimentation of fine-grained glaciolacustrine sediments and associated build-up of excess pore pressure. The second event was presumably triggered by a major earthquake (Mw≈7) in AD 1348 and comprises a mass-transport complex and several landslides, which led to a c. 30 cm thick turbidite. In total, 62 landslides are imaged in the multibeam map, 6 of which are most likely human-induced. Some of these show horseshoe-type compressional ridges and frontal breaching, whereas others exhibit an extensive zone of rafted blocks. We attribute these morphological differences to four main factors: (1) slope gradient and changes therein; (2) preconditioning of the impacted zone; (3) volume of remobilized sediment; and (4) type of impactor.

scholarly journals Thrust Faults Promoted Hydrocarbon Leakage at the Compressional Zone of Fine-Grained Mass-Transport Deposits

2021 ◽  
Vol 9 ◽  
Author(s):  
Qiliang Sun ◽  
Xinong Xie ◽  
Shiguo Wu ◽  
Guorui Yin
Keyword(s):  
Fluid Flow ◽  
Mass Transport ◽  
Northern South China Sea ◽  
Coarse Grained ◽  
Thrust Faults ◽  
Borehole Data ◽  
Fine Grained ◽  
Hydrocarbon Reservoir ◽  
Effective Seal ◽  
Mass Transport Deposits

Fine-grained mass-transport deposits (MTDs), especially their compressional toe zones, are traditionally considered as effective seal in constraining the vertical fluid migration underneath. However, this study documents thrust faults at the compressional toe zone of fine-grained MTDs that could disaggregate the seal competence and promote vertical fluid flow. The investigated MTD referred to as MTD-a lies directly over a large hydrocarbon reservoir that is located within the Central Canyon of northern South China Sea, which is examined by using high-resolution 3D seismic and borehole data. Thrust faults and irregular blocks composed of coarse-grained sandstones are observed in the compressional zone of the MTD-a’s toe. More importantly, seismic evidence (e.g., enhanced seismic reflections) suggests that a large amount of hydrocarbons from the underlying reservoir penetrated through the MTD-a along these thrust faults and charged into the coarse-grained sandstone blocks. This clear evidence of thrust faults compromising the MTD’s seal effectiveness and thus facilitating the vertical fluid flow through the non-permeable strata demonstrate the importance of reassessing the seal capacity of MTD.

scholarly journals Combined On-Fault and Off-Fault Paleoseismic Evidence in the Postglacial Infill of the Inner-Alpine Lake Achensee (Austria, Eastern Alps)

2021 ◽  
Vol 9 ◽  
Author(s):  
Patrick Oswald ◽  
Jasper Moernaut ◽  
Stefano C. Fabbri ◽  
Marc De Batist ◽  
Irka Hajdas ◽  
...  
Keyword(s):  
Seismic Hazard Assessment ◽  
Late Glacial ◽  
Eastern Alps ◽  
Alpine Lake ◽  
European Alps ◽  
Recurrence Rates ◽  
Active Deformation ◽  
Landscape Modification ◽  
Moderate Seismicity ◽  
Surface Ruptures

The Eastern European Alps are characterized by slow active deformation with low- to moderate seismicity. Recurrence rates of severe earthquakes exceed the time span of historical documentation. Therefore, historical and instrumental earthquake records might be insufficient for seismic hazard assessment and high-quality paleoseismic data is required. However, primary geological observations of postglacial fault activity are scarcely found, because major faults are buried below thick sedimentary sequences in glacially overdeepened valleys. Moreover, high erosion rates, gravitational slope processes and penetrative anthropogenic landscape modification often obscure geomorphic features related to surface ruptures. Here we present one of the rare paleoseismic data sets showing both on-fault evidence as subaqueous surface ruptures and off-fault evidence as multiple coeval mass-transport deposits (MTDs) and megaturbidites within a single high-resolution seismic-stratigraphic framework of the inner-alpine lake Achensee. Co-occurrence of on-fault and off-fault paleoseismic evidence on three stratigraphic levels indicates seismic activity with inferred moment magnitudes MW ∼6–6.5 of the local, lake-crossing Sulzgraben-Eben thrust at ∼8.3 ka BP and twice in Late Glacial times. Additional eight stratigraphic levels with only off-fault paleoseismic evidence document severe seismic shaking related to the historical MW ∼5.7 earthquake in Hall (CE 1670) and seven Holocene earthquakes, which have exceeded a local seismic intensity of ∼VI (EMS-98) at Achensee. Furthermore, we discuss natural and methodological influencing factors and potential pitfalls for the elaboration of a subaqueous paleoseismic record based on surface ruptures and multiple, coeval MTDs.

Evaluating the sealing potential of young and thin mass-transport deposits: Lake Villarrica, Chile

2019 ◽  
Vol 500 (1) ◽  
pp. 129-146 ◽  
Author(s):  
Jasper Moernaut ◽  
Gauvain Wiemer ◽  
Achim Kopf ◽  
Michael Strasser
Keyword(s):  
Shear Strength ◽  
Mass Transport ◽  
Pore Pressure ◽  
Sediment Cores ◽  
Free Fall ◽  
Undrained Shear Strength ◽  
Excess Pore Pressure ◽  
Minor Role ◽  
Mass Transport Deposits ◽  
Undrained Shear

AbstractSubaqueous mass-transport deposits (MTDs) can be important elements in hydrocarbon systems, forming potential reservoirs or seals. Most research has targeted outcrops or moderately to deeply buried MTDs and, therefore, the petrophysical properties of near-seafloor MTDs, and their influence in the trapping and release of shallow fluids, is poorly studied. Here, we investigate shallow MTDs in Lake Villarrica (Chile) by combining sub-bottom profiles, free-fall penetrometer data, pore pressure dissipation tests and geotechnical properties of sediment cores. Low undrained shear strength under a surficial MTD indicates underconsolidation caused by sudden loading and rapid sealing. Larger, buried MTDs show acoustic signatures of free gas at their base, indicating effective sealing. This is supported by degassing core gaps just below MTDs and by excess pore pressure ratios c. 30–70% within MTDs. Acoustic windows below rafted blocks suggest local fluid escape. MTDs exhibit elevated undrained shear strength and reduced porosity compared to surrounding sediments, but are comparable to upslope source sequences. This suggests that MTD sealing capacity in Villarrica relates to the apparently overconsolidated nature of the slope sequence, leaving a minor role for shear densification. This study shows that shallow MTDs can form a relatively rapid seal for fluid migration, locally degraded by rafted blocks.

scholarly journals Seismic control of large prehistoric rockslides in the Eastern Alps

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Patrick Oswald ◽  
Michael Strasser ◽  
Christa Hammerl ◽  
Jasper Moernaut
Keyword(s):  
Eastern Alps ◽  
European Alps ◽  
Rock Slopes ◽  
Seismic Control ◽  
Temporal Cluster ◽  
Multiple Datasets ◽  
Moderate Seismicity ◽  
Spatio Temporal ◽  
Epicentral Intensity

AbstractLarge prehistoric rockslides tend to occur within spatio-temporal clusters suggesting a common trigger such as earthquake shaking or enhanced wet periods. Yet, trigger assessment remains equivocal due to the lack of conclusive observational evidence. Here, we use high-resolution lacustrine paleoseismology to evaluate the relation between past seismicity and a spatio-temporal cluster of large prehistoric rockslides in the Eastern Alps. Temporal and spatial coincidence of paleoseismic evidence with multiple rockslides at ~4.1 and ~3.0 ka BP reveals that severe earthquakes (local magnitude ML5.5–6.5; epicentral intensity I0VIII¼–X¾) have triggered these rockslides. A series of preceding severe earthquakes is likely to have progressively weakened these rock slopes towards critical state. These findings elucidate the role of seismicity in preparing and triggering large prehistoric rockslides in the European Alps, where rockslides and earthquakes typically occur in clusters. Such integration of multiple datasets in other formerly glaciated regions with low to moderate seismicity will improve our understanding of catastrophic rockslide drivers.

scholarly journals Submarine mass wasting and associated tsunami risk offshore western Thailand, Andaman Sea, Indian Ocean

2012 ◽  
Vol 12 (8) ◽  
pp. 2609-2630 ◽  
Author(s):  
J. M. Schwab ◽  
S. Krastel ◽  
M. Grün ◽  
F. Gross ◽  
P. Pananont ◽  
...  
Keyword(s):  
Mass Transport ◽  
Andaman Sea ◽  
Excess Pore Pressure ◽  
Western Slope ◽  
Shelf Area ◽  
Submarine Landslides ◽  
Mass Wasting ◽  
Recurrence Rates ◽  
Mass Transport Deposits ◽  
Water Depths

Abstract. 2-D seismic data from the top and the western slope of Mergui Ridge in water depths between 300 and 2200 m off the Thai west coast have been investigated in order to identify mass transport deposits (MTDs) and evaluate the tsunamigenic potential of submarine landslides in this outer shelf area. Based on our newly collected data, 17 mass transport deposits have been identified. Minimum volumes of individual MTDs range between 0.3 km3 and 14 km3. Landslide deposits have been identified in three different settings: (i) stacked MTDs within disturbed and faulted basin sediments at the transition of the East Andaman Basin to the Mergui Ridge; (ii) MTDs within a pile of drift sediments at the basin-ridge transition; and (iii) MTDs near the edge of/on top of Mergui Ridge in relatively shallow water depths (< 1000 m). Our data indicate that the Mergui Ridge slope area seems to have been generally unstable with repeated occurrence of slide events. We find that the most likely causes for slope instabilities may be the presence of unstable drift sediments, excess pore pressure, and active tectonics. Most MTDs are located in large water depths (> 1000 m) and/or comprise small volumes suggesting a small tsunami potential. Moreover, the recurrence rates of failure events seem to be low. Some MTDs with tsunami potential, however, have been identified on top of Mergui Ridge. Mass-wasting events that may occur in the future at similar locations may trigger tsunamis if they comprise sufficient volumes. Landslide tsunamis, emerging from slope failures in the working area and affecting western Thailand coastal areas therefore cannot be excluded, though the probability is very small compared to the probability of earthquake-triggered tsunamis, arising from the Sunda Trench.

Quantitative paleoseismology in Carinthia, Eastern Alps: Calibrating the lacustrine sedimentary record with historical earthquake data

2020 ◽  
Author(s):  
Christoph Daxer ◽  
Christa Hammerl ◽  
Maria del Puy Papi-Isaba ◽  
Stefano Claudio Fabbri ◽  
Patrick Oswald ◽  
...  
Keyword(s):  
Mass Transport ◽  
Quantitative Description ◽  
Eastern Alps ◽  
Historical Earthquake ◽  
Sedimentary Record ◽  
Large Lakes ◽  
Intensity Pattern ◽  
Thin Sections ◽  
Moderate Seismicity ◽  
Mass Transport Deposits

&lt;p&gt;In intraplate settings with moderate seismicity, recurrence intervals of strong earthquakes (M&lt;sub&gt;w &lt;/sub&gt;&gt;6) typically exceed the short time span of instrumental and historical records. To assess the seismic hazard in such regions, lake sediments are increasingly used as earthquake archives: they can record strong seismic shaking as mass transport deposits (MTDs), turbidites or sediment deformations, preserved over several thousands of years. To provide information on paleo-earthquake size, however, the sedimentary imprints need to be thoroughly calibrated with independent information on seismic shaking strength.&lt;/p&gt;&lt;p&gt;In Carinthia (Eastern Alps, Austria), numerous lakes have experienced several devastating historical earthquakes with local seismic intensities (SI) ranging from V-XI (EMS-98 scale), although being located in an intraplate environment. Given that i) these events are well-spaced in time (AD1201, AD1348, AD1511, AD1690, AD1857 and AD1976), ii) due to historical earthquake research, an exceptional historical documentation exists, and iii) accurate shakemaps can be built based on a local Intensity Prediction Equation (IPE), we can examine the relationship between seismic intensity and the type, size and spatial distribution of sedimentary imprint in the lakes.&lt;/p&gt;&lt;p&gt;Here, we present investigations on two large lakes &amp;#8211; W&amp;#246;rthersee and Millst&amp;#228;tter See &amp;#8211; by a dense grid of reflection seismic profiles (~640 km overall), 80 short (~1.5 m) sediment cores and multibeam bathymetry. The lakes consist of several sub-basins with potentially different intensity thresholds for the generation of sedimentary imprints. Mapping of MTDs, their scarps and associated turbidites as well as accurate dating (radiocarbon and varve counting on sediment thin sections) shows that the AD1348 earthquake (M&lt;sub&gt;w&lt;/sub&gt; ~7) led to extensive slope failures in both lakes. The AD1511 (M&lt;sub&gt;w&lt;/sub&gt; ~6.9) and AD1690 (M&lt;sub&gt;w&lt;/sub&gt; ~6.5) events, which exhibited lower local intensities (~VII) compared to those of AD1348 (VIII), are recorded as minor MTDs and turbidites. Quantitative description of earthquake-related event deposits (cumulative turbidite thickness, volume of mass transport deposits/megaturbidites) suggests a linear correlation with the respective local intensities in both W&amp;#246;rthersee and Millst&amp;#228;tter See.&lt;/p&gt;&lt;p&gt;The AD1976 earthquake (M&lt;sub&gt;w&lt;/sub&gt; ~6.5; SI V-VI at the lakes) is not evidenced in the sedimentary record and therefore can be used for constraining the minimum threshold intensity for seismically-induced event deposits. By applying a grid-search approach using an empirical intensity-attenuation relationship, we can narrow down possible earthquake scenarios. Our data suggests that the highly debated epicentre of the AD1348 earthquake was much closer to the Austrian-Italian border than the epicentre of the AD1976 Friuli earthquake, possibly originating from the Periadriatic lineament. The AD1511 event probably had its epicentre southeast of our study area in Slovenia, and therefore further east than previous studies suggested. The AD1690 earthquake, however, is most likely of a local origin.&lt;/p&gt;&lt;p&gt;Our study reveals that investigating one lake, let alone one sediment core, is insufficient to reconstruct a region&amp;#8217;s seismic history. Due to the exceptional setting of Carinthia, however, we can constrain the intensity pattern and localise the most likely epicentral region and fault source of past earthquakes. In an ongoing interdisciplinary study, we use this calibration to construct long calibrated lacustrine records for the last 14 ka.&lt;/p&gt;

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