Geolunch seminar @ UiB

Prof. Claudio Valeriano
2018-06-06 13:15 - 14:00 (Europe/Oslo) | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
The Mariana mining dam rupture: isotope tracing of the iron rich mud from the largest environmental accident on Nov 2015 along the Doce River and adjacent marine environments.
Prof. Claudio Valeriano
On research gate: here

Prof. Monica Heilbron
2018-06-05 12:15 - 13:00 | Auditorium 5, 3rd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Evolution of the Brazilian continental margin and the link with Neoproterozoic orogens
Prof. Monica Heilbron (GeoAtlantico institute)
On research gate: here

Joyce Shi Sim
2018-05-23 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Large scale organization of melt focusing beneath mid-ocean ridges using new open-sourced two phase M3LT models
Author: Joyce Shi Sim
Magmatism at mid-ocean ridges generates new oceanic crust and accounts for 90% of global volcanism. The oceanic crust is emplaced in a narrow neo-volcanic region (e.g. Macdonald (1982); Carbotte et al. (2016)), whereas basaltic melt is generated in a wide region beneath mid-ocean ridges as
suggested by a few geophysical surveys (Forsyth et al., 1998b; Key et al.,
2013). A number of focusing mechanisms have been proposed such as ridge
suction (Spiegelman and McKenzie, 1987) and decompaction layers (Sparks
and Parmentier, 1991). We present results from a suite of two-phase mod-
els applied to the mid-ocean ridges with varying half spreading rate using
a new open source model, M3LT, to explore the dynamics of Melt in the
Mantle beneath Mid-ocean ridges (Sim et al., 2018). M3LT is built using
TerraFERMA (Wilson et al., 2017). The amount of oceanic crust versus
half spreading rate generated by our models are within observations from
active seismic surveys (White et al., 1992; Bown and White, 1994; White
et al., 2001; Harding et al., 2017). Our models suggest that the suppres-
sion of porosity waves with increasing half spreading rates contributes to
the decrease of oceanic crustal thickness variations. There are three melt
focusing mechanisms present in our models, namely: ridge suction from in-
compressible shear, decompaction layers and the recently discovered melting
rate focusing. Further analyses suggest that melting rate focusing decreases
slightly with spreading rate whereas melt focusing from decompaction lay-
ers increase rapidly below half spreading rate of 4 cm/yr and then decrease
slightly for half spreading rate more than 4 cm/yr. Melting rate focusing is
persistent regardless of spreading rates and it focuses a higher proportion of melt produced at slower spreading rates.

Timothy Cullen
2018-05-09 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
First insights into stratigraphic architecture in proximal deepwater syn-rift sediments in the hanging-wall of a rift margin border fault
Tim Cullen (VISTA Visitor from University of Leeds , PhD Student in the Syn Rift Systems Group)
Syn-rift deep-water sands represent a significant play type worldwide with recent exploration successes in the North Sea highlighting a need to further the understanding of stratigraphic architecture. Sediment dispersal patterns and the resultant stratigraphic architecture in syn-rift settings is complex and controlled by the interplay of topography, sediment supply and base-level changes, which are all highly variable spatially and temporally. Extensive outcrops surrounding the Xylokastro Horst in the Gulf of Corinth, Greece present an exceptional opportunity to investigate syn-rift deltas and a coeval deep-water clastic system deposited in the hanging wall of a rift margin border fault. The Early-to-Middle Pleistocene syn-rift stratigraphy comprises 400 m thick Evrostini/Ilias Gilbert type deltas located at fault segment boundaries along the northern flank of the Xylokastro Horst. The northern hanging-wall to the horst is filled with axially deflected gravity current deposits that are connected to the bottomsets of the deltas. The generation of a new stratigraphic scheme for the West Xylokastro Fault block from integrated fieldwork, digital outcrop modelling and core data from a research borehole will allow investigation of architectural changes in relation to key basin-evolution events such as fault activity and sea level fluctuations. Preliminary observations from the core show a variety of core expressions of outcrop stratigraphic architectures which further the application of these outcrops as reservoir analogues.
The outcrops of the Evrostini/Ilias deltas and gravity current deposits permit investigation of down-dip flow transformation in relation to seabed topography at bed-scale through to seismic- scale stacking patterns. The depositional architecture is complicated by the influence of multiple sediment sources, including what are thought to be laterally emplaced mass transport deposits. The significant facies and architectural variation are related to activity on both small and large rift structures, which have influenced the character of coarse-grained pinchouts in the distal parts of the system. An understanding of sand architecture can be gained in the context of a deforming basin-floor providing significant control on syn-rift reservoir distribution, highly analogous to current ongoing developments and exploration targets worldwide.

Thomas Theunissen
2018-05-02 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Long-term coupling and feedbacks between surface processes and tectonics during rifting: from proximal to distal domains
Thomas Theunissen, Ritske S. Huismans

Whereas significant efforts have been made to understand the relationship between mountain building and surface processes, limited research has been done on the relationship between surface processes and extensional tectonics. Here we present high-resolution 2-D coupled tectonic-surface processes modeling of extensional basin formation. The main aim is to find out how erosion and deposition affect the deformation in extensional systems. We test the combined effects of crustal rheology and varying surface process efficiency (erodibility, sea level) on structural style of rift and passive margin formation. The results show that both erosion of rift flank areas and basin deposition enhance localization of crustal deformation. Frictional-plastic extensional shear zones accumulate more deformation during a longer period of time, and loading of offshore basins can generate crustal ductile flow. Synthetic normal faults system in the proximal domain are enhanced by both erosion of footwall and deposition on the hangingwall. Feedbacks with distal margin formation are more contrasted. In case of wide margin, sediment export is limited as a results of absent rift flank topography. Sediment export to the distal margin is enhanced by a low sea level. In extreme cases sediment deposition delays lithospheric rupture. In case of narrow margin, sedimentation on distal margin can enhance extreme thinning. These mechanisms are enhanced when fluvial erosion, transport and deposition are efficient. We show that removal of mass from rift flanks and sedimentary loading in the basin area provide a first order feedback with tectonic deformation and control on rifted margin tectonic-morphology. However, surface processes do not change the first order structural style of rifting, which is largely controlled by crustal rheology. Rift escarpment morphology is function of paleo-topography and sea level. Variation of strain localization in natural rift systems correlates with the observed behavior and suggests similar feedbacks as demonstrated by the forward numerical models.

Sebastian Wolf
2018-04-25 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
From small and cold to large and hot orogens: How do they grow and what are the influences of extensional inheritance and surface processes?
Authors: Sebastian G. Wolf, Ritske S. Huismans, Peter van der Beek
In this geolunch I will show you our recent work on mountain building, where we have been using numerical models to understand the archetypical evolution of an orogen on Earth.
During recent years, geodynamic models have underpinned our understanding of the growth of a mountain belt from a small, cold to a large, hot orogen as a function of the amount of convergence. Additionally, studies have demonstrated that the structural style of a mountain belt is strongly influenced by inherited weak (extensional) structures, the amount of erosion and deposition, as well as the distribution of shallow detachment horizons. We use upper-mantle scale plane-strain thermo-mechanical models coupled to a 2D, mass conserving surface process model (FastScape), to investigate the long-term evolution of mountain belts and the influence of extensional inheritance and surface processes thereon.
With our models we can establish an evolutionary framework for orogenic growth from a monovergent wedge to an orogenic plateau, and find that internal crustal loading is the main driver for the evolution. Extensional inheritance and simple surface processes modify the structures, but have no first order mechanical influence.
T-model snapshot. Top: Surface processes with FastScape; bottom: Thermo-mechanical solution from Fantom

Leonardo Muniz Pichel
2018-04-18 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Impacts of Pre-Salt Relief on Differential Translation, Diapirism and Post-Salt Tectono-Stratigraphy

Thilo Wrona
2018-04-04 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Soon…

Magnhild Sydnes
2018-03-21 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Magmatic intrusions and structural developments effect on temperature and maturation in sedimentary basins
Magmatic intrusions are emplaced in many sedimentary basins throughout the world. From the Norwegian continental shelf they are known to be present in the Norwegian Sea and the Barents Sea. The Vøring Basin in the Norwegian Sea, is known for its numerous intruded sills. Magmatic sills can be relatively easy to spot on seismic as they stand out due to their high acoustic impedance. However, determining their thickness, their upper and lower boundaries, can be challenging due to seismic resolution. This has consequences for thermal and maturation modeling in areas with magmatic intrusions.
Generally sills are emplaced in structurally complex areas. When sills intrude, the magma may be ~1000°C intruding into a system which is under development. The basin has already been through stages of structural changes, and more changes will occur after the emplacement of sills. To understand sills effect on temperature and maturation in basins, it is necessary to have a good knowledge of the structural development and its affect on the temperature evolution, also before the sills intruded. Standard basin modeling does not have the ability to reconstruct the structural evolution of basins, nor (to my knowledge) the ability to implement sills into the modeling. I will present results performed by a high resolution 2D basin modeling software able to conduct both structural reconstruction of basins and study the effect of emplaced sills.
Source: Sydnes et al., 2018

Thomas Phillips
2018-03-14 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
The influence of pre-existing structures on the geometry and evolution of rift systems – Case studies from offshore southern Norway
Structural heterogeneities are ubiquitous throughout the earth’s crust and upper mantle, and as such have been proposed to exert fundamental controls on the geometry and evolution of rift systems. However, the geometry of these heterogeneities is often poorly defined and their geometric and kinematic links to superposed rift systems simply based on 2D plan-view correlations.
In this talk, I use 2D and 3D seismic reflection data to investigate a series of pre-existing structures located offshore south Norway, and examine the interactions, or lack thereof, with the superposed rift. In the west, we identify a series of intrabasement structures which, based on their seismic character and 3D geometry, are correlated to onshore Devonian shear zones. These shear zones show a range of different styles of structural inheritance with later rift-related faults. To the east, we interpret a dyke swarm on seismic reflection data, and show that this can act as a mechanical template for the formation of later faults. Finally, we examine the upper crustal expression of a sub-crustal lineament, the Sorgenfrei-Tornquist Zone, which corresponds to a change in lithospheric thickness. The upper-crustal expression of this lineament is repeatedly reactivated during later tectonic events, with the style of this reactivation reflective of the prevailing regional stress field.
Pre-existing structures, situated at various levels throughout the lithosphere, show a range of different interactions with rift-related faults. Those within the upper crust may dictate the geometry and evolution of individual faults in some cases, but be offset in others; whereas pre-existing structures at deeper levels are associated with complex, periodically reactivated, upper-crustal rift systems.
Schematic models showing the 3 major types of interactions between intrabasement structures and rift-related faults. From left to right; Merging faults, Exploitative faultsand Cross-cutting faults.

Antoine Turquet
2018-03-06 14:15 - 15:00
Quantifying location uncertainties in seismicity catalogs: Application to the Pyrennees.

Antoine L. Turquet, Thomas Bodin, Pierre Arroucau, Matthieu Sylvander, Kevin Manchuel

There are plenty of methods available for locating earthquakes. Linearised least squared optimisation methods are commonly used to construct seismicity catalogues, as they are fast and simple to implement. These methods are based on minimising the root- mean-square (RMS) of the travel time residuals to find best fitting location coordinates and origin time. There are two well known problems reducing the quality of estimation: (1) the linearisation of the inverse problem causes dependence on the initial guess, (2) regularisation of the velocity matrix gives solutions and eventually the error ellipses that can vary with the chosen damping coefficient. For example, one can artificially move the source position towards the initial guess location and decrease the size of the error by simply increasing the damping parameter. In this work, we propose a method to quantify unbiased uncertainties with a series of synthetic tests. We first generate travel times for events from all possible coordinates on a 3D grid and then locate each synthetic event by using HYPOCENTER software (this can be applied to any location method). Finally, we produce a 3D error map, where at each grid point, we plot the location error, i.e. the distance between the event at the given grid point and its inverted location. Furthermore, we show how this error map vary with the quantity and quality of data, and with user-defined parameters. We are also providing a methodology to tune the seismic location parameters and calculate the corresponding uncertainties for this set of parameters for the professionals who are using similar earthquake location softwares.

Hasbi Ash Shiddiqi
2018-02-21 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Source study of the 24 August 2016 Chauk earthquake, Myanmar
The source process of an intra-slab intermediate depth earthquake (h=92 km) that occurred near Chauk, Central Myanmar on 24 August 2016 was investigated using teleseismic body-wave inversion. The focal mechanism solution showed a thrust mechanism with nearly vertical or sub-horizontal fault planes. The slip inversion results for both fault planes gives similar variances and show a simple slip distribution. The fault-plane ambiguity was resolved by analyzing apparent source time functions for teleseismic stations affected by the directivity effect. Based on this analysis, we prefer the sub-horizontal fault plane where the rupture propagated down-dip. The T-axis showed down-dip extension while the P-axis showed slab normal compression. We obtained an effective fault length = 21.9 km and effective fault width = 18.1 km. A Stress drop of 20 bars was estimated by using the relation of effective fault dimension and seismic moment obtained from the slip inversion. Furthermore, we tested the stress drop, and the assumption of quality factor, which is adopted from another subduction zone, by conducting the earthquake ground motion modeling at five regional strong motion stations. A stress drop of 20 bars can produce reasonable ground motion for these stations. One of the most prevailing hypothesis of the generating mechanism of sub-horizontal faulting in intermediate-depth is related to the dehydration embrittlement which either reactivated an existing fault before it was subducted or newly created fault after, e.g., due to slab unbending processes.

Nicolas Riel
2018-02-14 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Cancelled

Sebastian Wolf
2018-02-07 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway

Bjørn Nyberg
2018-01-31 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
The Global Distribution of Rivers to Terrestrial Sinks: its Spatial and Temporal Control on Alluvial Systems
An important component in the spatial and temporal discharge of sediment to oceans is terrestrial sedimentary sinks that act as buffers and sequestrate sediments and nutrients along its river route. The implications of which have a wide range of importance including shaping landscapes, mountain building processes, water-atmosphere interactions, biochemical cycles, ecological and biological influences, water resources and socio-economic concern. However, to our knowledge, a global catchment model depicting the drainage patterns of modern rivers to terrestrial sedimentary basins does not currently exist.
Here we propose a new global terrestrial sink catchment (GTSC) database that delineates the distribution of high-resolution global river networks in relation to mapped modern terrestrial sedimentary basins. The results show that the morphology of source catchments contributing to its terrestrial sedimentary basin is different by tectonic regimes. Distinctions in catchment characteristics influence system response to change, terrestrial sediment transit times and along strike variability in sink composition of alluvial systems. Furthermore, the distribution and character of source catchments has a direct influence on human settlement and regulation practices of water resources.
Figure 1 – The global terrestrial sink catchment (GTSC) database depicting source catchment contributions to modern terrestrial sedimentary basins.

Eric Salomon
2018-01-24 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Asymmetric continental deformation along southern Brazil and Namibia during South Atlantic rifting and its influence on Paraná-Etendeka Large Igneous Province emplacement
Plate restoration of South America and Africa to their pre-breakup position faces the problem of gaps and overlaps between the continents, an issue commonly solved with implementing intra-plate deformation zones within South America. One of these zones is often positioned at the latitude of SE/S Brazil. However, geological evidence for the existence of a distinct zone in this region is lacking. Obvious instead is that SE/S Brazil has been affected by the outpour of the voluminous Paraná-Etendeka Large Igneous Province. These lavas are closely linked to the South Atlantic opening, and of which 93 % are emplaced in and around southern Brazil and 7 % in Namibia on the African side.
In this presentation I will show, that combining published data on various geological aspects pictures a distinctive asymmetric deformation of the onshore passive margin of SE/S Brazil and its conjugate margin of NW Namibia. Whereas Namibia experienced margin-perpendicular extension during breakup, SE/S Brazil was subject to margin-parallel extension. Based on these observations, I will propose a breakup model that helps solving the apparent misfit in plate reconstructions in this region and at the same time explains the highly unequal distribution of the Paraná-Etendeka Large Igneous Province between South America and Africa.

AGU practice talks 2017
2017-12-06 00:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Coming soon…

Johannes Wiest
2017-11-29 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
The concept “Metamorphic Core Complex” and its application in SW Norway
First proposed in the late 1970s, the field-based concept of metamorphic core complexes (MCCs) has evolved into a fundamental mode of lithosphere extension. The worldwide identification of MCCs in different geodynamic settings strongly influenced the understanding of extensional tectonics, but the concept remains highly controversial and far from fully understood. In this presentation, I will summarize the evolution of the MCC concept and its implications for lithosphere rheology. Based on recent review articles, I present important conceptual models as well as latest advances concerning core-complex dynamics. In the light of new results from fieldwork in the Øygarden Complex, I will discuss how the concept MCC might enhance our understanding of post-Caledonian extensional tectonics in SW Norway.

Jan Michalek
2017-11-22 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Svalbard Ultra Reconnaissance Expedition (SURE 2017) from Aug-Sep 2017
Coming soon…

Nicolas Riel
2017-11-08 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Postponed to 2nd semester !

Thomas Theunissen
2017-11-01 00:15 - 13:00
Mantle exhumation at magma-poor rifted margin: a competition between frictional shear zones and thermally weakened necking domains. Consequences on time of breakup at Galicia/Newfoundland margins.
Theunissen Thomas, Huismans Ritske S.
Here we present a new analysis and interpretation of basement topography of the transitional domain from continental to oceanic crust along the conjugate margin sections SCREETCH-1 (Newfoundland) and WE-1/ISE-1 (Galicia Bank). The absence of significant syn-rift magmatism in this area allows using 2-D thermo-mechanical modelling to understand the formation of the distal margin and exhumed mantle. We show that plastic strain weakening of the exhumed mantle is required to explain observations on basement morphology, and detachment faulting. Our models predict that the evolution of detachment faulting within the transitional domain depends on the degree of frictional-plastic strain-weakening and varies from a single unique steady state asymmetric low angle detachment fault for large degree of strain weakening to multiple out-of-sequence forming detachments with or without dip reversal for lower amounts of strain-weakening. The model behaviour is a consequence of the competition between weak frictional-plastic shear zones and the thermally weakened necking domain in the footwall. The forward models reproduce elevations, wavelength of exhumed mantle ridges for a narrow range of rift velocities between 10 and 15 mm/yr and considering the increasing thermal conductivity of peridotites at shallow depth. This causes an efficient cooling of the footwall that has then enough strength to support high topography. The forward models also predict that the peridotite ridge is the breakaway of a second detachment fault that dates the crustal breakup and that rocks on top of the peridotite ridge have experimented a fast cooling (< 2 Ma). We use predictions from these forward models to discuss time of breakup and the position of the first steady state oceanic ridge at Galicia/Newfounland conjugate margins.
A: Distal part of the seismic profile WE-1 on Iberia side. B: Distal part of the seismic profile SREETCH-1 on New-Foundland side.

Isabel Edmundson
2017-10-25 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Structural geometries associated with extension, inversion and strike slip deformation; insights from field observations along the northern Somerset coast, southwest UK.

Several kilometre long sections of the northern Somerset coastline showcase excellent exposures of faults and associated structures within the Triassic and Lower Jurassic. The combination of low tides uncovering cliffs and wave cut platforms, and a complex structural history documented by multiple outcrops ensure that this coastline is a popular destination for geologists. It was for these reasons that myself, David Peacock, Dave Sanderson, Vilde Dimmen and two master’s students arranged a three day field trip to this coastline. The trip provided an opportunity for the two students to carry out reconnaissance for their projects, and for myself and Vilde to see more field examples of fault structures that could complement our own PhD projects. It is hoped that this informal presentation will give an insight into how field observations can help to improve understanding of fault geometry and associated deformation as a result of extension and subsequent reactivation.
The area has a complicated tectonic history having been affected by several structural phases beginning with N-S orientated compression during the Variscan orogeny. This event established the dominant E-W trending structural grain along which periods of later extension and compression would follow. The first of three discrete rift events occurred in the Permian, the second in the early Jurassic and the third in the late Jurassic to early Cretaceous, each indicated by wedge thickening geometries. Following this protracted period of rifting, N-S compression associated with the Alpine orogeny in the late Cretaceous reversed the sense of motion along established E-W Mesozoic faults. Tightening of roll over anticlines previously established by extension and a Lower Cretaceous regional angular unconformity provides evidence for this event. Finally, strike-slip reactivation of NW-SE trending faults during the Miocene established several pull apart basins indicating a sinistral sense of displacement. Many of the observed outcrops document this restructuring but are generally below seismic resolution. However, recent research has shown that many fault systems and associated geometries are scale independent and so small scale examples can provide good analogues for larger scale structures observed on seismic. In addition to this, many features of faults and associated damage zones are not visible on seismic, reducing the fault to a simple feature. Consequently, the complexity of the fault and fault related deformation can be overlooked, yet these features have important implications for fluid flow and should be remembered during interpretation and modelling.

Photograph showing the hangingwall anticline formed by inversion of a south dripping extensional fault in the Lower Jurassic shales and limestones. Cliff is ~50m high.

Vivi Pedersen
2017-10-04 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Earth surface processes: interacting with the solid Earth, ice and sea level
Surface processes change the Earth surface dramatically and interact with the solid Earth, ice, and thereby also global sea level. For instance, changes in topography due to glacial erosion will influence ice-sheet configuration and dynamics. The deep glacial erosion in fjords will also cause erosional unloading and result in solid-Earth deformation. In addition, solid-Earth deformation will influence topography and therefore the first-order behaviour of surface processes.
In this seminar, I will exemplify these interactions, first with a strong focus on the formation and evolution of topography. In particular, I will target the outstanding question related to high topography at passive continental margins, where the importance of surface processes and solid-Earth deformation is still debated.
Secondly, I will elaborate on the importance of surface processes for sea level research, through their interaction with the solid Earth and ice sheets. Both a changed topography and solid-Earth deformation has the potential to influence the response of ice sheets to climate change, and thereby ice-sheet stability and sea level.

Kuvvet Atakan and other
2017-09-27 00:15 - 13:00
M 8.1 – 87km SW of Pijijiapan, Mexico
https://earthquake.usgs.gov/earthquakes/eventpage/us2000ahv0#executive
Opened discussion about this unusual major normal earthquake (MW8.1 – 70 km depth).
The September 8th, 2017, M 8.1 earthquake offshore Chiapas, Mexico, occurred as the result of normal faulting at an intermediate depth. Focal mechanism solutions for the earthquake indicate slip occurred on either a fault dipping very shallowly towards the southwest, or on steeply dipping fault striking NW-SE. At the location of this event, the Cocos plate converges with North America at a rate of approximately 76 mm/yr, in a northeast direction. The Cocos plate begins its subduction beneath Central America at the Middle America Trench, just over 100 km to the southwest of this earthquake. The location, depth, and normal-faulting mechanism of this earthquake indicate that it is likely an intraplate event, within the subducting Cocos slab, rather than on the shallower megathrust plate boundary interface.
While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal-faulting events of the size of the September 8th, 2017 earthquake are typically about 200×50 km (length x width).
Over the preceding century, the region within 250 km of the hypocenter of the September 8th, 2017 earthquake has experienced 8 other M 7+ earthquakes. Most occurred in the subduction zone to the southeast of the September 8 event, near the Mexico-Guatemala border, and none were larger than M 7.5. The largest, a M 7.4 thrust faulting earthquake offshore Guatemala in November 2012, resulted in at least 48 fatalities and over 150 injuries, and significant damage near the coast.

Star: epicenter of the mainshock. Gray and white dots: historical seismicity epicenters.

Thilo Wrona
2017-09-13 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Seismic facies analysis using machine learning
Thilo Wrona1, Håkon Fossen1, Robert L. Gawthorpe1, Indranil Pan2
1Department of Earth Science, University of Bergen, Norway
2Department of Earth Science and Engineering, Imperial College London, UK
Seismic interpretations are, by definition, subjective and often require significant time and expertise from the interpreter. We demonstrate that machine learning techniques can help address these problems by performing seismic facies analyses in a rigorous, reproducible way. For this purpose, we use state-of-the-art 3D broadband seismic reflection data of the northern North Sea. Our workflow includes five basic steps. First, we extract seismic attributes to highlight features in the data. Second, we perform a manual seismic facies classification on 1000 examples. Third, we use some of these examples to train a range of models to predict seismic facies. Fourth, we analyze the performance of these models on the remaining examples. Fifth, we select the ‘best’ model (i.e. highest accuracy) and apply it to a seismic section. As such, we highlight that machine learning techniques can increase the efficiency and reproducibility of seismic facies analyses.

Tristan Salles (USyd)
2017-06-27 12:15 - 13:00 | Auditorium 5, 3rd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Adding stratigraphy to landscape evolution model: basin architecture on passive margins & peneplain preservation
First, I will present new results on the influence of dynamic topography on passive continental margin stratigraphy. Quantifying the interaction between surface processes and tectonics/deep Earth processes has been one important aspect of landscape evolution modelling in recent decades. Both observations and results from numerical modelling indicate that dynamic topography plays a significant role in shaping landscape through geological time. Recent research suggests that dynamic topography also has non-negligible effects on stratigraphic architecture by modifying accommodation space available for sedimentation. Using Badlands I will investigate the evolution of a continental scale landscape in response to transient dynamic uplift or subsidence, and model the stratigraphic development (looking at stratal stacking pattern, vertical cross-sections and wheeler diagram) on passive continental margins in response to sea-level change, thermal subsidence and dynamic topography.
Then, I will discuss using newly implemented erosion laws the role of bedload fluxes on the preservation of low-relief summit surfaces. Low relief upland areas form summit surfaces in many dissected mountain ranges. They are often distinguished by their conspicuous flatness compared to the surrounding dissected terrain. Such relict landscape generate two questions: 1, is preservation a random process, or is there a process that helps such surfaces to resist dissection, and 2, how come relict landscapes are generally exclusively composed of subdued terrain? Dissection of the landscape by renewed wave of incision is controlled by river erosive power. River incision is achieved by various processes, but one of the main contributors is bedrock abrasion by bedload. Here I will show how this process can explain the persistence of subdued topographies.

Rosa Polanco-Ferrer
2017-06-07 12:15 - 13:00
Title: TBA

Jeff Prancevic
2017-05-31 12:15 - 13:30 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
The influence of hillslope angle on landslide initiation and the occurrence of threshold hillslopes
The concept of threshold hillslopes has been widely applied to both soil-mantled and bedrock landscapes, postulating that once hillslopes achieve the critical topographic gradient where landslides dominate erosion they cannot steepen further. This process transition has been used to explain observations of ubiquitous modal hillslopes that cluster around values of 35° to 40° in steep landscapes globally, despite wide variability of climate, erosion rate, and soil characteristics. However, there is no clear explanation for why ~35° is the special slope towards which landscapes adjust. Landslides start occurring at slopes that are much lower (~20°), and the angle of repose of weathered bedrock is generally much steeper (45°+). In this study we use a series of laboratory landslide experiments and observations of landslide scars to examine how hillslope gradient affects the occurrence of landslides. Surprisingly, we find that similar runoff rates are required to initiate landslides at all hillslope gradients between 25° and 45°. The ubiquitous modal hillslope gradient of 35° sits in the middle of this range of gradients that are similarly susceptible to landslide initiation. Because hillslope gradients tend to be normally distributed, a modal hillslope gradient of 35° places the greatest portion of the landscape within the landslide regime. If landslides, specifically those caused by large rainfall events, are the most efficient mode of erosion, then a distribution of hillslope gradients that sits in the middle of this process regime should generate the fastest possible erosion rates.

Timm John
2017-05-24 12:15 - 13:30 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Ultra high pressure rocks – a window into metamorphic processes occurring in subduction zones

Anneleen Guerts
2017-04-05 12:15 - 13:00
TBA
