342 research outputs found
Occurrence of partial and total coseismic ruptures of segmented normal fault systems: insights from the Central Apennines, Italy
No full textNormal faulting earthquakes rarely rupture the entire extent of active normal faults, and can also jump between neighbouring faults. This confounds attempts to use segmentation models to define the likelihood of future rupture scenarios. We attempt to study this problem comparing the offsets produced in single earthquakes with those produced by multiple earthquakes over longer timescales, together with detailed studies of the structural geology. We study the active normal fault system causative of the Mw 6.3 2009 L’Aquila earthquake in central Italy, comparing the spatial distribution of coseismic offsets, cumulative offsets that have developed since 15 ±3 ka, and the total offsets that have accumulated since the faults initiated at 2-3 Ma. Our findings suggest that: 1) faults within a segmented fault system behave as a single interacting fault segment over time periods including multiple earthquake cycles (e.g. 2-3 Ma or 15±3ka), with single earthquakes causing either partial or total ruptures of the entire system; 2) an along-strike bend causes throw and throw-rates enhancements within the bend throughout the seismic history of the fault system. We discuss the synchronised and geometrically controlled activity rates on these faults in terms of the propensity for floating earthquakes, multi-fault earthquakes, and seismic hazard
Slip distributions on active normal faults measured from LiDAR and field mapping of geomorphic offsets: an example from L'Aquila, Italy, and implications for modelling seismic moment release
No full textSurface slip distributions for an active normal fault in central Italy have been measured using terrestrial laser scanning (TLS), in order to assess the impact of changes in fault orientation and kinematics when modelling subsurface slip distributions that control seismic moment release. The southeastern segment of the surface trace of the Campo Felice active normal fault near the city of L'Aquila was mapped and surveyed using techniques from structural geology and using TLS to define the vertical and horizontal offsets of geomorphic slopes since the last glacial maximum (15 ± 3 ka). The fault geometry and kinematics measured from 43 sites and throw/heave measurements from geomorphic offsets seen on 250 scarp profiles were analysed using a modification of the Kostrov equations to calculate the magnitudes and directions of horizontal principal strain-rates. The map trace of the studied fault is linear, except where a prominent bend has formed to link across a former left-stepping relay-zone. The dip of the fault and slip direction are constant across the bend. Throw-rates since 15 ± 3 ka decrease linearly from the fault centre to the tip, except in the location of the prominent bend where higher throw rates are recorded. Vertical coseismic offsets for two palaeo earthquake ruptures seen as fresh strips of rock at the base of the bedrock scarp also increase within the prominent bend. The principal strain-rate, calculated by combining strike, dip, slip-direction and post 15 ± 3 ka throw rate, decreases linearly from the fault centre towards the tip; the strain-rate does not increase across the prominent fault bend. The above shows that changes in fault strike, whilst having no effect on the principal horizontal strain-rate, can produce local maxima in throw-rates during single earthquakes that persist over the timescale of multiple earthquakes (15 ± 3 ka). Detailed geomorphological and structural characterisation of active faults is therefore a critical requirement in order to properly define fault activity for the purpose of accurate seismic hazard assessment. We discuss the implications of modelling subsurface slip distributions for earthquake ruptures through inversion of GPS, InSAR and strong motion data using planar fault approximations, referring to recent examples on the nearby Paganica fault that ruptured in the Mw 6.3 2009 L'Aquila Earthquake
Slip on a mapped normal fault for the 28th December 1908 Messina earthquake (Mw 7.1) in Italy
No full textThe 28th December 1908 Messina earthquake (Mw 7.1), Italy, caused >80,000 deaths and transformed
earthquake science by triggering the study of earthquake environmental effects worldwide, yet its
source is still a matter of debate. To constrain the geometry and kinematics of the earthquake we use
elastic half-space modelling on non-planar faults, constrained by the geology and geomorphology of
the Messina Strait, to replicate levelling data from 1907–1909. The novelty of our approach is that we
(a) recognise the similarity between the pattern of vertical motions and that of other normal faulting
earthquakes, and (b) for the first time model the levelling data using the location and geometry of a
well-known offshore capable fault. Our results indicate slip on the capable fault with a dip to the east of
70° and 5 m dip-slip at depth, with slip propagating to the surface on the sea bed. Our work emphasises
that geological and geomorphological observations supporting maps of capable non-planar faults
should not be ignored when attempting to identify the sources of major earthquakes
Horizontal strain-rates and throw-rates across breached relay zones, central Italy: implications for the preservation of throw deficits at points of normal fault linkage
No full textIn order to investigate the relationship between the throws and 3D orientation of breaching faults crossing relay zones, kinematic data, throw-rates and total throws have been measured for an active normal fault in the Italian Apennines that displays a relay zone at its centre. The c. 0.8 km long breaching fault dips at 67 ± 5° and strikes obliquely to c. 2–3 km long faults outside the relay zone which dip at 61 ± 5°. Total throws of pre-rift limestone define a throw profile with a double maximum (370 ± 50 m; 360 ± 50 m) separated by an area of lower throw (100 ± 50 m) where the breaching fault is growing. Throw-rates implied by offsets across bedrock scarps of Late Pleistocene–Holocene landforms (15 ± 3 ka) are higher across the breaching fault (0.67 ± 0.13 mm/yr) than for locations of throw maxima on the neighbouring faults (0.38 ± 0.07 mm/yr; 0.55 ± 0.11 mm/yr). The deficit in total throw will be removed in 0.68–1.0 Myr if these deformation rates continue. To investigate why the highest throw-rates occur in the location with lowest total throw, Kostrov horizontal strain-rate tensors were calculated in 1 × 2 km boxes. We show that the oblique strike and relatively high dip of the breaching fault mean that it must have a relatively high throw-rate in order for it to have a horizontal strain-rate concomitant with its position at the centre of the overall fault. We show that whether throw minima at locations of fault linkage are preserved during progressive fault slip depends on the 3D orientation of the breaching fault. We use the above to discuss the longevity of throw deficits and multiple throw maxima along faults in relation to seismic hazard and landscape evolution
4-HYDROXY PHENYL ETHANOL (p-TYROSOL) AND ITS SINGLY HYDRATED COMPLEX
No full text M.R. Hockridge, S.M. Knight, E.G. Robertson, J.P. Simons, J. McCombie and M. Walker Phys. Chem. Chem. Phys. 1, 407-413 1999.Author Institution: School of Chemistry, University of Nottingham, Nottingham, UK; Physical and Theoretical Chemisry Laboratory, South Parks Road, Oxford, UKThe conformational structures of 4-hydroxy phenol ethanol (p-tyrosol) and it's 1:1 hydrated cluster, have been characterised in a free jet expansion through a combination of mass-selected, resonantly enhanced two-photon ionisation (MS-R2PI), fluorescence excitation and ultra-violet `hole-burning' spectroscopy, together with rotational contour analysis and ab initio . It has been possible to assign the structures of both the gauche cis and gauche trans OH rotamers, as well as the extended anti conformer, and their 1:1 hydrated clusters. The `tagging' of the phenolic OH group by the hydrogen-bonded water molecule also allows unambiguous assignment of the cis and trans gauche conformers through rotational band contour analysis
Relationship between topography, rates of extension and mantle dynamics in the actively-extending Italian Apennines
No full textTo investigate the mechanism driving active extension in the central and southern Italian Apennines and the geography of seismic hazard, we compare spatial variations in upper crustal strain-rate measured across exposed fault scarps since 15 ± 3 ka with data on cumulative upper-crustal strain and topographic elevation, and free-air gravity, P-wave tomography and SKS splitting delay times that are a proxy for strain in the mantle. High extensional strain-rates across the Apennines since 15 ± 3 ka (0.4–3.1 mm/yr along 90 km transects) occur in two areas (Lazio-Abruzzo; SE Campania and Basilicata) where values for finite extensional strains that have developed since 2–3 Ma are highest (2–7 km cumulative throw), and where mean elevation in 5 × 90 km NE–SW boxes is > 600 m; the intervening area (NW Campania and Molise) with < 600 m mean elevation in 5 × 90 km boxes has extension-rates < 0.4 mm/yr and lower values for finite extensional strains (< 2 km cumulative throw). These two areas with high upper-crustal strain-rates overlie mantle that has relatively-long spatially-interpolated SKS delay times (1.2–1.8 s) indicating relatively-high mantle strains and free-air gravity values (140–160 mGals); the intervening area of lower extension-rate has shorter spatially-interpolated SKS delay times (0.8–1.2 s) and lower free-air gravity values (120 mGals). The two areas with high upper crustal strain-rates and strain, mean elevation, and mantle strain, coincide with the northern and southern edges of a slab window in the Tyrrhenian–Apennines subducting plate that has been inferred from published P-wave tomography. Together these correlations suggest that dynamic support of the topography by mantle flow through the slab window may control the present day upper crustal strain-rate field in the Apennines and the geography of seismic hazard in the region
CAVITY RING DOWN SPECTROSCOPY OF CARBON CHAIN RADICALS
No full textT. Motylewski and H. Linnartz, Rev. Sci, Instrum. 70, 1305(1999). T. Motylewski, H. Linnartz, O. Vaizert, J.P. Maier, G.A. Galazutdinov, F.A. Musaev, J. Krelowski, G.A.H. Walker, and D.A. Bohlender, Astrophys. J. 531, xxxx(2000)Author Institution: Department of Physical Chemistry, University of BaselCavity ring down spectroscopy through a supersonic planar plasma is used to study the electronic transitions of a series of carbon chain radicals in direct The gas phase spectra of species of the form , , , and are compared to the hitherto reported diffuse interstellar band positions
Multi-millennia slip rate relationships between closely spaced across-strike faults: Temporal earthquake clustering of the Skinos and Pisia Faults, Greece, from in situ 36Cl cosmogenic exposure dating
No full textThis study investigates slip behaviour on overlapping, en echelon normal faults by analysing the slip histories of the Skinos and Pisia active normal faults over the past ∼20 kyrs using in situ 36Cl cosmogenic dating. New 36Cl data from the Skinos Fault and published Pisia Fault 36Cl data were modelled, with both sample sites located within an overlap zone and separated by an across-strike distance of 1–2 km. Our analysis reveals fluctuating slip rates, with the two faults alternating between out-of-phase and simultaneous slip. The Pisia Fault exhibited a slip rate of ∼0.5–0.75 mm/yr from ∼20 ka to ∼9.6 ka, increasing to ∼1.25 mm/yr until ∼5.2 ka. It then slowed to ∼0.25 mm/yr or less until ∼2.0 ka, before accelerating again to ∼1.25–1.5 mm/yr to the present day. The Skinos Fault maintained a low slip rate of ∼0.25 mm/yr or less from ∼20 ka to ∼6.4 ka, before accelerating to ∼2.0–3.0 mm/yr, persisting to ∼1.0 ka or possibly the present-day. Comparing their slip histories, the faults show periods of simultaneous slip between ∼6.4 ka to ∼5.2 ka and ∼2.0 ka to ∼1.0–0.0 ka, and out-of-phase slip occurred between ∼9.6 ka and ∼6.4 ka, and from ∼5.2 ka to ∼2.0 ka. Out-of-phase behaviour on faults across strike has now been observed on faults spaced across-strike at distances of 1–2 km, 10–20 km, and ∼100 km, raising the question of why it occurs. Possible mechanism(s), including rheological fluctuations within fault/shear-zone structures linked between the brittle upper crust and viscous lower crust and stress interactions, are discussed to explain the out-of-phase and simultaneous slip behaviour.This work was supported by the Natural Environment Research Council with a studentship awarded to Sam Mitchell [grant number NE/S007229/1] and grant to Prof. Gerald Roberts, Prof. Joanna Faure Walker, and Dr. Zoë Mildon [grant number NE/VO12894/1]. We thank Manuel Curzi and an anonymous reviewer for helping to improve the manuscript
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