TY - JOUR A1 - Spooner, Cameron A1 - Scheck-Wenderoth, Magdalena A1 - Cacace, Mauro A1 - Anikiev, Denis T1 - How Alpine seismicity relates to lithospheric strength JF - International journal of earth sciences N2 - Despite the amount of research focussed on the Alpine orogen, different hypotheses still exist regarding varying spatial seismicity distribution patterns throughout the region. Previous measurement-constrained regional 3D models of lithospheric density distribution and thermal field facilitate the generation of a data-based rheological model of the region. In this study, we compute the long-term lithospheric strength and compare its spatial variation to observed seismicity patterns. We demonstrate how strength maxima within the crust (similar to 1 GPa) and upper mantle (> 2 GPa) occur at temperatures characteristic of the onset of crystal plasticity in those rocks (crust: 200-400 degrees C; mantle: similar to 600 degrees C), with almost all seismicity occurring in these regions. Correlation in the northern and southern forelands between crustal and lithospheric strengths and seismicity show different patterns of event distribution, reflecting their different tectonic settings. Seismicity in the plate boundary setting of the southern foreland corresponds to the integrated lithospheric strength, occurring mainly in the weaker domains surrounding the strong Adriatic plate. In the intraplate setting of the northern foreland, seismicity correlates to modelled crustal strength, and it mainly occurs in the weaker and warmer crust beneath the Upper Rhine Graben. We, therefore, suggest that seismicity in the upper crust is linked to weak crustal domains, which are more prone to localise deformation promoting failure and, depending on the local properties of the fault, earthquakes at relatively lower levels of accumulated stress than their neighbouring stronger counterparts. Upper mantle seismicity at depths greater than modelled brittle conditions, can be either explained by embrittlement of the mantle due to grain-size sensitive deformation within domains of active or recent slab cooling, or by dissipative weakening mechanisms, such as thermal runaway from shear heating and/or dehydration reactions within an overly ductile mantle. Results generated in this study are available for open access use to further discussions on the region. KW - lithosphere KW - strength KW - rheology KW - 3D-Model KW - Alps KW - seismicity Y1 - 2022 U6 - https://doi.org/10.1007/s00531-022-02174-5 SN - 1437-3254 SN - 1437-3262 VL - 111 IS - 4 SP - 1201 EP - 1221 PB - Springer CY - Berlin ; Heidelberg ER - TY - JOUR A1 - Rodriguez Piceda, Constanza A1 - Scheck-Wenderoth, Magdalena A1 - Cacace, Mauro A1 - Bott, Judith A1 - Strecker, Manfred T1 - Long-Term Lithospheric Strength and Upper-Plate Seismicity in the Southern Central Andes, 29 degrees-39 degrees S JF - Geochemistry, geophysics, geosystems N2 - We examined the relationship between the mechanical strength of the lithosphere and the distribution of seismicity within the overriding continental plate of the southern Central Andes (SCA, 29 degrees-39 degrees S), where the oceanic Nazca Plate changes its subduction angle between 33 degrees S and 35 degrees S, from subhorizontal in the north (<5 degrees) to steep in the south (similar to 30 degrees). We computed the long-term lithospheric strength based on an existing 3D model describing variations in thickness, density, and temperature of the main geological units forming the lithosphere of the SCA and adjacent forearc and foreland regions. The comparison between our results and seismicity within the overriding plate (upper-plate seismicity) shows that most of the events occur within the modeled brittle domain of the lithosphere. The depth where the deformation mode switches from brittle frictional to thermally activated ductile creep provides a conservative lower bound to the seismogenic zone in the overriding plate of the study area. We also found that the majority of upper-plate earthquakes occurs within the realm of first-order contrasts in integrated strength (12.7-13.3 log Pam in the Andean orogen vs. 13.5-13.9 log Pam in the forearc and the foreland). Specific conditions characterize the mechanically strong northern foreland of the Andes, where seismicity is likely explained by the effects of slab steepening. KW - subduction zone KW - Andes KW - rheology KW - seismicity KW - flat-slab Y1 - 2022 U6 - https://doi.org/10.1029/2021GC010171 SN - 1525-2027 VL - 23 IS - 3 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Spooner, Cameron A1 - Scheck-Wenderoth, Magdalena A1 - Cacace, Mauro A1 - Götze, Hans-Jürgen A1 - Luijendijk, Elco T1 - The 3D thermal field across the Alpine orogen and its forelands and the relation to seismicity JF - Global and planetary change N2 - Temperature exerts a first order control on rock strength, principally via thermally activated creep deformation and on the distribution at depth of the brittle-ductile transition zone. The latter can be regarded as the lower bound to the seismogenic zone, thereby controlling the spatial distribution of seismicity within a lithospheric plate. As such, models of the crustal thermal field are important to understand the localisation of seismicity. Here we relate results from 3D simulations of the steady state thermal field of the Alpine orogen and its forelands to the distribution of seismicity in this seismically active area of Central Europe. The model takes into account how the crustal heterogeneity of the region effects thermal properties and is validated with a dataset of wellbore temperatures. We find that the Adriatic crust appears more mafic, through its radiogenic heat values (1.30E-06 W/m3) and maximum temperature of seismicity (600 degrees C), than the European crust (1.3-2.6E-06 W/m3 and 450 degrees C). We also show that at depths of < 10 km the thermal field is largely controlled by sedimentary blanketing or topographic effects, whilst the deeper temperature field is primarily controlled by the LAB topology and the distribution and parameterization of radiogenic heat sources within the upper crust. KW - steady-state KW - thermal-field KW - Europe KW - Alps KW - Adria KW - seismicity Y1 - 2020 U6 - https://doi.org/10.1016/j.gloplacha.2020.103288 SN - 0921-8181 SN - 1872-6364 VL - 193 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kober, Florian A1 - Zeilinger, Gerold A1 - Hippe, Kristina A1 - Marc, Odin A1 - Lendzioch, Theodora A1 - Grischott, Reto A1 - Christl, Marcus A1 - Kubik, Peter W. A1 - Zola, Ramiro T1 - Tectonic and lithological controls on denudation rates in the central Bolivian Andes JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - The topographic signature of a mountain belt depends on the interplay of tectonic, climatic and erosional processes, whose relative importance changes over times, while quantifying these processes and their rates at specific times remains a challenge. The eastern Andes of central Bolivia offer a natural laboratory in which such interplay has been debated. Here, we investigate the Rio Grande catchment which crosses orthogonally the eastern Andes orogen from the Eastern Cordillera into the Subandean Zone, exhibiting a catchment relief of up to 5000 m. Despite an enhanced tectonic activity in the Subandes, local relief, mean and modal slopes and channel steepness indices are largely similar compared to the Eastern Cordillera and the intervening Interandean Zone. Nevertheless, a dataset of 57 new cosmogenic 10Be and 26AI catchment wide denudation rates from the Rio Grande catchment reveals up to one order of magnitude higher denudation rates in the Subandean Zone (mean 0.8 mm/yr) compared to the upstream physiographic regions. We infer that tectonic activity in the thrusting dominated Subandean belt causes higher denudation rates based on cumulative rock uplift investigations and due to the absence of a pronounced climate gradient. Furthermore, the lower rock strength of the Subandean sedimentary units correlates with mean slopes similar to the ones of the Eastern Cordillera and Interandean Zone, highlighting the fact, that lithology and rock strength can control high denudation rates at low slopes. Low denudation rates measured at the outlet of the Rio Grande catchment (Abapo) are interpreted to be a result of a biased cosmogenic nuclide mixing that is dominated by headwater signals from the Eastern Cordillera and the Interandean zone and limited catchment sediment connectivity in the lower river reaches. Therefore, comparisons of short- (i.e., sediment yield) and millennial denudation rates require caution when postulating tectonic and/or climatic forcing without detailed studies. (C) 2015 The Authors. Published by Elsevier B.V. KW - Rio Grande KW - seismicity KW - uplift KW - rock strength KW - cosmogenic nuclides KW - denudation Y1 - 2015 U6 - https://doi.org/10.1016/j.tecto.2015.06.037 SN - 0040-1951 SN - 1879-3266 VL - 657 SP - 230 EP - 244 PB - Elsevier CY - Amsterdam ER - TY - THES A1 - Zöller, Gert T1 - Critical states of seismicity : modeling and data analysis T1 - Kritische Zustände seismischer Dynamik : Modellierung und Datenanalyse N2 - The occurrence of earthquakes is characterized by a high degree of spatiotemporal complexity. Although numerous patterns, e.g. fore- and aftershock sequences, are well-known, the underlying mechanisms are not observable and thus not understood. Because the recurrence times of large earthquakes are usually decades or centuries, the number of such events in corresponding data sets is too small to draw conclusions with reasonable statistical significance. Therefore, the present study combines both, numerical modeling and analysis of real data in order to unveil the relationships between physical mechanisms and observational quantities. The key hypothesis is the validity of the so-called "critical point concept" for earthquakes, which assumes large earthquakes to occur as phase transitions in a spatially extended many-particle system, similar to percolation models. New concepts are developed to detect critical states in simulated and in natural data sets. The results indicate that important features of seismicity like the frequency-size distribution and the temporal clustering of earthquakes depend on frictional and structural fault parameters. In particular, the degree of quenched spatial disorder (the "roughness") of a fault zone determines whether large earthquakes occur quasiperiodically or more clustered. This illustrates the power of numerical models in order to identify regions in parameter space, which are relevant for natural seismicity. The critical point concept is verified for both, synthetic and natural seismicity, in terms of a critical state which precedes a large earthquake: a gradual roughening of the (unobservable) stress field leads to a scale-free (observable) frequency-size distribution. Furthermore, the growth of the spatial correlation length and the acceleration of the seismic energy release prior to large events is found. The predictive power of these precursors is, however, limited. Instead of forecasting time, location, and magnitude of individual events, a contribution to a broad multiparameter approach is encouraging. N2 - Das Auftreten von Erdbeben zeichnet sich durch eine hohe raumzeitliche Komplexität aus. Obwohl zahlreiche Muster, wie Vor- und Nachbeben bekannt sind, weiß man wenig über die zugrundeliegenden Mechanismen, da diese sich direkter Beobachtung entziehen. Die Zeit zwischen zwei starken Erdbeben in einer seismisch aktiven Region beträgt Jahrzehnte bis Jahrhunderte. Folglich ist die Anzahl solcher Ereignisse in einem Datensatz gering und es ist kaum möglich, allein aus Beobachtungsdaten statistisch signifikante Aussagen über deren Eigenschaften abzuleiten. Die vorliegende Arbeit nutzt daher numerische Modellierungen einer Verwerfungszone in Verbindung mit Datenanalyse, um die Beziehung zwischen physikalischen Mechanismen und beobachteter Seismizität zu studieren. Die zentrale Hypothese ist die Gültigkeit des sogenannten "kritischen Punkt Konzeptes" für Seismizität, d.h. starke Erdbeben werden als Phasenübergänge in einem räumlich ausgedehnten Vielteilchensystem betrachtet, ähnlich wie in Modellen aus der statistischen Physik (z.B. Perkolationsmodelle). Es werden praktische Konzepte entwickelt, die es ermöglichen, kritische Zustände in simulierten und in beobachteten Daten sichtbar zu machen. Die Resultate zeigen, dass wesentliche Eigenschaften von Seismizität, etwa die Magnitudenverteilung und das raumzeitliche Clustern von Erdbeben, durch Reibungs- und Bruchparameter bestimmt werden. Insbesondere der Grad räumlicher Unordnung (die "Rauhheit") einer Verwerfungszone hat Einfluss darauf, ob starke Erdbeben quasiperiodisch oder eher zufällig auftreten. Dieser Befund zeigt auf, wie numerische Modelle genutzt werden können, um den Parameterraum für reale Verwerfungen einzugrenzen. Das kritische Punkt Konzept kann in synthetischer und in beobachteter Seismizität verifiziert werden. Dies artikuliert sich auch in Vorläuferphänomenen vor großen Erdbeben: Die Aufrauhung des (unbeobachtbaren) Spannungsfeldes führt zu einer Skalenfreiheit der (beobachtbaren) Größenverteilung; die räumliche Korrelationslänge wächst und die seismische Energiefreisetzung wird beschleunigt. Ein starkes Erdbeben kann in einem zusammenhängenden Bruch oder in einem unterbrochenen Bruch (Vorbeben und Hauptbeben) stattfinden. Die beobachtbaren Vorläufer besitzen eine begrenzte Prognosekraft für die Auftretenswahrscheinlichkeit starker Erdbeben - eine präzise Vorhersage von Ort, Zeit, und Stärke eines nahenden Erdbebens ist allerdings nicht möglich. Die genannten Parameter erscheinen eher vielversprechend als Beitrag zu einem umfassenden Multiparameteransatz für eine verbesserte zeitabhängige Gefährdungsabschätzung. KW - Seismizität KW - Erdbebenvorhersage KW - statistische Physik KW - mathematische Modellierung KW - Datenanalyse KW - seismicity KW - earthquake prediction KW - statistical physics KW - mathematical modeling KW - data analysis Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-7427 ER -