Mechanics of continental extension from Quaternary strain fields in the Italian Apennines

Horizontal upper crustal surface strain-rates calculated using slip-vectors from striated faults and offsets of Late Pleistocene-Holocene landforms and sediments are used to investigate the mechanisms responsible for deformation in the Italian Apennines over a variety of length-scales ranging from individual fault segments up to the width of the mountain range. The method used allows strain-rates in any 5km \times 5km grid square or combination of these grid squares to be calculated. This allows comparison of strain-rates from 15 \pm 3 kyrs of slip with those from shorter time periods within polygons that are comparable in size, shape and location with those imposed by geodetic station locations or moment summation calculations. Strain-rates over a time period of 15 \pm 3 kyrs from 5km \times 5km grid squares integrated over an area of 1.28 \times 10^4 km^2 (80km \times 160 km), show the horizontal strain-rate of the Lazio-Abruzzo region of the central Apennines is 1.18^{+0.12} _{-0.04}\times10^{-8}yr^{-1} and -1.83^{+3.80} _{-4.43}\times10^{-10}yr^{-1} parallel and perpendicular to the regional principal strain direction (043^o-223^o \pm 1^o), associated with extension rates of \leq3.1^{+0.7} _{-0.4} mm yr^{-1} if calculated in boxes with a 5km width and 90km length across the Apennines. In Molise-North Campania, the horizontal principal strain-rate calculated over an area of 5\times10^3 km^2 (50km\times100 km) is 2.11^{+1.14} _{-0.16}\times10^{-9} yr^{-1} along the horizontal axis parallel to 039^o - 219^o \pm 3^o, and 0.88^{+2.84}_{-1:30}\times10^{-10} yr^{-1} perpendicular to it, associated with extension rates of \leq0.2^{+0.2} _{-0.1} mm yr^{-1} if calculated in 5km \times 90km transects that cross the Apennines. Within the South Campania-Basilicata region of the southern Apennines of area 8 \pm 103 km2 (50km_160 km), the average horizontal strain-rate over 15 \pm 3 kyrs is 3.70\pm0.26\times10^{-9} yr^{-1} parallel to and 3.65\pm2.05\times10^{-10} mmyr^{-1} perpendicular to the principal strain axis (044^o-224^o\pm2^o), associated with extension rates of \leq0.6\pm0.2mmyr^{-1} if calculated in 5km\times90km transects across the Apennines. The same method is used to calculate strain-rates in Calabria from longerterm offset geological features (\leq 580 ka); the horizontal principal strain-rate calculated over an area of 8\times103 km^2 (40km\times200 km) is 6.71\pm2.13\times10^{-9} yr^{-1} along the horizontal axis parallel to 086^o-226^o\pm3^o, and -8.40\pm5.69\times10^{-10} yr^{-1} perpendicular to it. Strain-rates calculated over 15\pm3 kyrs within 5km\times5km grid squares vary from zero up to 2.34\pm0.54\times10^{-7} yr^{-1}, 3.69\pm1.33\times10^{-8} yr^{-1}, and 1.20\pm0.41\times10^{-7} yr^{-1} in the central Apennines, the Molise-North Campania region, and the southern Apennines, respectively. These strain-rates resolve variations in strain orientations and magnitudes along the strike of individual faults and are used to produce a fault specific earthquake recurrence interval map. In order to study the existence of possible deficits or surpluses of geodetic and earthquake strain in the Apennines, these 15 \pm 3 kyrs multi seismic cycle strain-rates have been compared to short-term strain-rates calculated using geodesy (over 126 yrs, 11 yrs and 5 yrs) and seismic moment summation (over 700 yrs). Regional strain-rates calculated from geodesy and historical earthquakes are greater than those calculated from offset 15 \pm 3 ka landforms and sediments. In detail, 10^{1-2} yr strain-rates are higher than 10^4 yr strain-rates in some small areas (\approx2000 km^2, corresponding to polygons defined by geodesy campaigns and seismic moment summations) with the opposite situation in other areas where seismic moment release rates in large (Ms>6.0) magnitude historical earthquakes have been reported to be as low as zero. This demonstrates (1) the importance of comparing the exact same areas, and (2) that strain-rates vary spatially on the length-scale of individual faults and on a timescale between 10^{1-2} yrs and 10^4 yrs in the Apennines. The results are used to discuss temporal earthquake clustering and the natural variability of the seismic cycle. Spatial variations in upper crustal strain-rate measured across exposed fault scarps since 15\pm3 ka are also used to discuss the regional deformation related to plate boundary and sub-crustal forces, specifically, whether mantle upwelling and uplift contribute to forces associated with the active extension in the Italian Apennines. Strain-rates calculated in 5km \times 90km boxes across the Apennines are compared with data on cumulative upper-crustal strain, topography, free-air gravity and SKS splitting delay times that are a proxy for strain in the mantle. High extension-rates across the Apennines since 15 \pm 3 ka (0.4-3.1mm yr^{-1}) occur in the southern Apennines and central Apennines where values for finite extensional strains that have developed since 2-3Ma are highest (2-7km cumulative throw), and where mean topography from SRTM data (Shuttle Radar Topography Mission) is > 600m; the intervening area of Molise-North Campania with < 600m topography has extension-rates < 0.4mm yr^{-1} and lower values for finite extensional strains (< 2km cumulative throw). These two areas with high upper-crustal extension-rates overlie mantle that has relatively-long spatially-interpolated SKS delay times (1.2-1.8 seconds) and relatively-high free-air gravity values of 140-160 mGals; the intervening area of lower extension-rates has relatively-low spatially-interpolated SKS delay times of 0.8-1.2 seconds and relatively-low free-air gravity values of 120 mGals. These correlations suggest that at the regional length-scale, a sub-crustal process, that is, dynamic support of the topography by mantle upwelling, controls the present-day upper-crustal strain-rate field in the Apennines and the geography of seismic hazard in the region. At a smaller length-scale, in 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.0.8km long breaching fault, investigated in detail, dips at 67^o\pm5^o and strikes obliquely to c.2-3km long faults outside the relay zone which dip at 61^o\pm5^o.Total throws of pre-rift limestone define a throw profile with a double maximum (370\pm50 m; 360\pm50 m) separated by an area of lower throw (100\pm50 m) where the breaching fault is growing. Throw-rates implied by offsets across bedrock scarps of Late Pleistocene-Holocene landforms (15 \pm 3 ka) are higher across the breaching fault (0.67\pm0.13mm yr^{-1}) than for locations of throw maxima on the neighbouring faults (0.38\pm0.07mm yr^{-1}; 0.55\pm0.11mm yr^{-1}). The deficit in total throw will be removed in 0.68-1.0 Myrs if these deformation rates continue. To investigate why the highest throw-rates occur in the location with lowest total throw, horizontal strain-rate tensors were calculated in 1km \times 2km boxes. It is shown 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. It is shown that whether throw minima at locations of fault linkage are preserved during progressive fault slip depends on the 3D orientation of the breaching fault. The above is used to discuss the longevity of throw deficits and multiple throw maxima along faults in relation to seismic hazard and landscape evolution. Overall, this thesis shows that calculation of horizontal strain-rates using the method developed herein, supported by collection of field data from active faults, can provide new insights into regional mechanisms of continental extension, seismic hazard, the seismic cycle, and fault growth; it provides a test of the hypothesis that earthquake recurrence is spatially random, providing evidence that instead, earthquake recurrence shows a spatial pattern that is controlled by fault evolution and sub-crustal processes

Warning and evacuation, case studies from Japan, Philippines and Dominica

In order to be effective, warning systems need to both reach those at risk and prompt appropriate action. We study the efficacy of early warning systems in prompting residents to take appropriate action ahead of severe hazards in island countries that experience regular disasters, namely following the Great East Japan Earthquake and Tsunami in Japan, Typhoon Yolanda in The Phillippines, and Hurricane Maria in Dominica. All these events were extreme in their impact and in addition had aspects which surprised residents such as the size of the tsunami, the strom surge and the late change in intensity which provided challenges with warning. We find that multiple forms of warning are needed in order for the whole population to be reached as no one form of warning reaches everyone. The timing of the warning is important for evacuation decisions including who stays and who evacuates. It is important that the whole cycle of a warning system is considered, and that it is viewed as a process, such that we consider the scientific, communications, social and infrastructure aspects of warning systems

Cash in a housing context: Transitional shelter and recovery in Japan

This paper presents city dwellers and local authorities with questions that international humanitarian organisations (IHOs) may not ask after massive housing destruction. We examine Japan's transitional shelter strategy following the 2011 Great East Japan Earthquake and Tsunami (GEJET) against these questions: who decides when and where to build housing; what is built, how and by whom; who finances, owns or rents; and how might such conditions affect disaster response? The analysis puts strategy in context by combining data on housing, subsidies and insurance, rather than presenting shelter delivery in isolation. In Japan, systemic housing-related vulnerabilities preceded the GEJET; shelter was a time-limited accommodation service; and cash hand-outs were not a cultural norm, not intended to be sufficient and never equivalent to the cost of temporary housing units. We argue that such analysis is needed to challenge IHO thinking and uncover specific historical, regulatory and personal housing trajectories following a disaster

A method for determining the suitability of schools as evacuation shelters and aid distribution hubs following disasters: case study from Cagayan de Oro, Philippines

Despite the controversy regarding their use, school buildings are often assigned as emergency evacuation shelters, temporary accommodation and aid distribution hubs following disasters. This paper presents a methodology to compare the relative suitability of different school buildings for these purposes by using the analytical hierarchy process to weight criteria based on the combined opinions of relevant experts and combine these with descriptive scores from surveyed buildings. The aggregated weights show that approximately equal weighting should be given to the hard characteristics (hazard at location and physical vulnerability) and soft characteristics (accessibility, communications, living environment, access to supplies). As well as immediate safety, conditions for inhabitation are important so that displaced persons are not discouraged from evacuating to shelters and shelter life is not detrimental to health and well-being. The study allows an optimal selection of school buildings used as shelters before and after a disaster and highlights where most improvement could be made with relatively little time and resources for both individual buildings and the whole study area. This method was applied to Cagayan de Oro in the Philippines, an area exposed to floods, windstorms and earthquakes, but can be adapted for other local contexts and building types. Among the 38 school buildings surveyed, we identified key areas for improvement as being insufficient pedestrian access for evacuation at night and for those with mobility constraints, and a lack of alternate spaces for evacuee activities leading to interference with education

Coulomb stress transfer and fault interaction over millennia on non-planar active normal faults: TheMw 6.5-5.0 seismic sequence of 2016-2017, central Italy

In order to investigate the importance of including strike-variable geometry and the knowledge of historical and palaeoseismic earthquakes when modelling static Coulomb stress transfer and rupture propagation, we have examined the August-October 2016 A.D. and January 2017 A.D. central Apennines seismic sequence (Mw 6.0, 5.9, 6.5 in 2016 A.D. (INGV) and Mw 5.1, 5.5, 5.4, 5.0 in 2017 A.D. (INGV)).We model both the coseismic loading (from historical and palaeoseismic earthquakes) and interseismic loading (derived from Holocene fault slip-rates) using strike-variable fault geometries constrained by fieldwork. The inclusion of the elapsed times from available historical and palaeoseismological earthquakes and on faults enables us to calculate the stress on the faults prior to the beginning of the seismic sequence. We take account the 1316-4155 yr elapsed time on the Mt. Vettore fault (that ruptured during the 2016 A.D. seismic sequence) implied by palaeoseismology, and the 377 and 313 yr elapsed times on the neighbouring Laga and Norcia faults respectively, indicated by the historical record. The stress changes through time are summed to show the state of stress on the Mt. Vettore, Laga and surrounding faults prior to and during the 2016-2017 A.D. sequence. We show that the build up of stress prior to 2016 A.D. on strike-variable fault geometries generated stress heterogeneities that correlate with the limits of the main-shock ruptures. Hence, we suggest that stress barriers appear to have control on the propagation and therefore the magnitudes of the main-shock ruptures

Uncertainty in strain-rate from field 1 measurements of the geometry, rates and kinematics of active normal faults: implications for seismic hazard assessment

Multiple measurements of the geometry, kinematics and rates of slip across the Auletta fault (Campania, Italy) are presented, and we use these to determine: (1) the spatial resolution of field measurements needed to accurately calculate a representative strain-rate; (2) what aspects of the geometry and kinematics would introduce uncertainty with regard to the strain-rate if not measured in the field. We find that the magnitude of the post last-glacial maximum throw across the fault varies along strike. If such variations are unnoticed, different values for a representative strain-rate, hence different results in seismic hazard calculations, would be produced. To demonstrate this, we progressively degrade our dataset, calculating the implied strain-rate at each step. Excluding measurements can alter strain-rate results beyond 1σ uncertainty, thus we urge caution when using only one measurement of slip-rate for calculating hazard. We investigate the effect of approximating the throw profile along the fault with boxcar and triangular distributions and show that this can underestimate or overestimate the strain-rate, with results in the range of 72-237% of our most detailed strain-rate calculation. We discuss how improved understanding of the potential implied errors in strain-rate calculations from field structural data should be implemented in seismic hazard calculations

Throw-rate variations within linkage zones during the growth of normal faults: case studies from the Western Volcanic Zone, Iceland.

This work investigates how throw-rates vary within fault bends and sites of fault linkage during the process of normal fault growth. In the Western Volcanic Zone, Iceland, through detailed field mapping and field measurements of fault throws, normal faults are mapped and along-strike throw profiles are constructed in order to understand how the throw-rates relate with the local fault geometry along faults at different stages of linkage. The results show that throw-rates increase within linkage zones and propagating fault bends independently from the stage of maturity of the fault bend. This implies that 1) the relationship between the local fault geometry and the along-strike distribution of throw-rate is driven by the deeper part of the fault, where established fault bends start propagating to the surface; 2) faults grow first by linkage and coalescence of separate faults, and then by accumulation of slip on the resultant fault, in agreement with models of fault growth by linkage and coalescence; 3) incipient fault bends can produce uncertainty associated with palaeoseismological results, if fault bends remain unrecognised. Moreover, this work demonstrates that existing models showing increased co-seismic and throw-rates within fault bends and sites of fault linkage found in continental extensional settings are valid in a geodynamic context of a mid-oceanic rifts

The Introduction of the Prevent Duty into Schools and Colleges: Stories of Continuity and Change

Drawing on mixed methods research carried out with school and college staff during 2015 and 2016, this chapter provides insight into how the Prevent Duty ‘landed’ in schools and colleges during the first 18 months after its introduction in July 2015. The discussion centres on four key questions: (1) To what extent did staff express overall opposition to or support for the Prevent Duty? (2) To what extent was the Prevent Duty interpreted by staff in schools and colleges as a straightforward extension of existing safeguarding responsibilities? (3) To what extent did staff perceive the Duty to be exacerbating the stigmatisation of Muslim students? (4) To what extent did staff perceive the Duty to have a ‘chilling effect’ on classrooms and on student voices

Fault2SHA Central Apennines database and structuring active fault data for seismic hazard assessment

We present a database of field data for active faults in the central Apennines, Italy, including trace, fault and main fault locations with activity and location certainties, and slip-rate, slip-vector and surface geometry data. As advances occur in our capability to create more detailed fault-based hazard models, depending on the availability of primary data and observations, it is desirable that such data can be organized in a way that is easily understood and incorporated into present and future models. The database structure presented herein aims to assist this process. We recommend stating what observations have led to different location and activity certainty and presenting slip-rate data with point location coordinates of where the data were collected with the time periods over which they were calculated. Such data reporting allows more complete uncertainty analyses in hazard and risk modelling. The data and maps are available as kmz, kml, and geopackage files with the data presented in spreadsheet files and the map coordinates as txt files. The files are available at: https://doi.org/10.1594/PANGAEA.922582

Slip distributions on active normal faults measured from LiDAR and field mapping of geomorphic offsets: an example from L\u2019Aquila, Italy, and implications for modelling seismic moment release

Surface 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\u2019Aquila 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 \ub13 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 is constant across the bend. Throw-rates since 15 \ub13 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 palaeoearthquake 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 \ub13 ka throw, 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 \ub13 ka). Detailed geomorphological and structural investigation of active faults is therefore a critical input 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\u2019Aquila Earthquak