
Gerald P RobertsBirkbeck, University of London · Department of Earth and Planetary Sciences
Gerald P Roberts
PhD Durham
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165
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Introduction
I am a full Professor of Earthquake Geology.
Publications
Publications (165)
Tectonically raised paleoshorelines have been recently identified along the southern
fault scarps of the Mt. Fellino and Roccarainola horst blocks, which are part of the
northeastern border of the Campania Plain coastal basin (southern Apennines, Italy).
Such horst blocks are bounded to the south by the Polvica Fault, a roughly E-W
trending normal...
Plain Language Summary
Slip rates of active faults are used in seismic hazard assessment to infer the frequency of damaging earthquakes. However slip rates are known to be variable when measured using different methodologies (e.g., geodesy, geomorphology) and timescales (years to millennia) for many types of faults in a range of tectonic settings....
Uncertainty concerning the processes responsible for slip-rate fluctuations associated with temporal clustering of
surface faulting earthquakes is a fundamental, unresolved issue in tectonics, because strain-rates accommodated
by fault/shear-zone structures are the key to understanding the viscosity structure of the crust and seismic
hazard. We con...
The relationships between kinematics and fault geometry for the coseismic ruptures from the 24th and 25th February 1981 earthquake sequence in the eastern Gulf of Corinth (Ms 6.7 and 6.4) are analysed. The two earthquakes ruptured faults located across strike rather than along strike as typifies other earthquake sequences. In detail, surface ruptur...
We model Coulomb stress transfer (CST) due to 30 strong earthquakes occurring on normal faults since 1509 CE in Calabria, Italy, including the influence of interseismic loading, and compare the results to existing studies of stress interaction from the Central and Southern Apennines, Italy. The three normal fault systems have different geometries a...
Cross‐cutting relationships and the incision history for multiple outflow channels have been mapped and studied to establish their relative chronology in Grjótá Valles, Mars, in order to establish whether observed geomorphic channels were formed in a single event or multiple events. The relative chronology can be established by mapping cross‐cuttin...
Surface faulting earthquakes are known to cluster in time from historical and palaeoseismic studies, but the mechanism(s) responsible for clustering, such as fault interaction, strain-storage, and evolving dynamic topography, are poorly quantified, and hence not well understood. We present a quantified replication of observed earthquake clustering...
We have mapped and constrained the timing of tectonically deformed uplifted Late Quaternary palaeoshorelines in the Messina Strait, southern Italy, an area above a subduction zone containing active normal faults. The palaeoshorelines are preserved from up to thirteen Late Quaternary sea-level highstands, providing a record of the deformation over t...
Cosmogenic exposure data can be used to calculate time‐varying fault slip rates on normal faults with exposed bedrock scarps. The method relies on assumptions related to how the scarp is preserved, which should be consistent at multiple locations along the same fault. Previous work commonly relied on cosmogenic data from a single sample locality to...
Quaternary uplift is well documented in SE Sicily, a region prone to damaging seismic events, such as the 1693 “Val di Noto” earthquake (Mw 7.4), the largest seismic event reported within the Italian Earthquake Catalogue, whose seismogenic source is still debated and, consequently, the long‐term seismic hazard is poorly understood. However, the spa...
Whether the stress-loading of faults to failure in earthquakes appears to be random or to an extent explainable, given constraints on fault/shear-zone interaction and the build-up and release of stress over many earthquake cycles, is a key question for seismic hazard assessment. Here we investigate earthquake recurrence for a system of 25 active no...
The geometry, rates and kinematics of active faulting in the region close to the tip of a major crustal-scale normal fault in the Gulf of Corinth, Greece, are investigated using detailed fault mapping and new absolute dating. Fault offsets have been dated using a combination of ²³⁴U/²³⁰Th coral dates and in situ ³⁶Cl cosmogenic exposure ages for se...
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 re...
The 2016–2017 Amatrice-Norcia seismic sequence was triggered by the reactivation of a complex NNW-SSE trending, WSW-dipping normal fault system cross-cutting the Umbria-Marche fold and thrust belt near M. Vettore. This fault system produced clear and impressive co-seismic ruptures on normal faults in the hangingwall of the M. Sibillini thrust, wher...
Successive locations of individual large earthquakes (Mw>5.5) over years to centuries can be difficult to explain with simple Coulomb Stress Transfer (CST) because it is common for seismicity to circumvent nearest-neighbour along-strike faults where coseismic CST is greatest. We demonstrate that Coulomb pre-stress (the cumulative CST from multiple...
The 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 to...
Following observations of mobilized boulder trail populations from Cerberus Fossae, Mars, that have been interpreted as possible evidence of large‐magnitude marsquakes rupturing for distances of ~207 km along exposed active faults, additional boulder trail populations were measured along shorter faults within the region of Grjota Valles (50‐ to 150...
Over the past 20 years, analyzing the abundance of the isotope chlorine-36 (36Cl) has emerged as a popular tool for geologic dating. In particular, it has been observed that 36Cl measurements along a fault plane can be used to study the timings of past ground displacements during earthquakes, which in turn can be used to improve existing seismic ha...
It has been suggested that a better knowledge of fault locations and slip-rates improves seismic hazard assessments. However, the importance of detailed along-fault slip-rate profiles and variable fault geometry has not yet been explored. We quantify the importance for modeled seismicity rates of using multiple throw-rate measurements to construct...
Large continental earthquakes necessarily involve failure of multiple faults or segments. But these same critically-stressed systems sometimes fail in drawn-out sequences of smaller earthquakes over days or years instead. These two modes of failure have vastly different implications for seismic hazard and it is not known why fault systems sometimes...
Successive locations of individual large earthquakes (Mw>5.5) over years to centuries can be difficult to explain with simple Coulomb stress transfer (CST), because seismicity can miss out nearest-neighbour along-strike faults where coseismic CST increases are greatest. We show that “Coulomb pre-stress” may explain this, because magnitudes are >±50...
Over the past twenty years, analyzing the abundance of the isotope chlorine-36 (³⁶Cl) has emerged as a popular tool for geologic dating. In particular, it has been observed that ³⁶Cl measurements along a fault plane can be used to study the timings of past ground displacements during earthquakes, which in turn can be used to improve existing seismi...
In order to investigate deformation within the upper plate of the Calabrian subduction zone we have mapped and modelled a sequence of Late Quaternary palaeoshorelines tectonically‐deformed by the Capo D’Orlando normal fault, NE Sicily, which forms part of the actively deforming Calabrian Arc. In addition to the 1908 Messina Strait earthquake (Mw 7....
Active extension within convergent margins results in spatially-variable uplift that overprints the regional uplift contribution linked to the subduction zone. The activity of these extensional faults can be examined using deformed marine terraces which record spatial variations in uplift and allow us to calculate the slip rates of active faults to...
In order to investigate deformation within the upper plate of the Calabrian subduction zone we have mapped and modelled a sequence of Late Quaternary palaeoshorelines tectonically‐deformed by the Capo D’Orlando normal fault, NE Sicily, which forms part of the actively deforming Calabrian Arc. In addition to the 1908 Messina Strait earthquake (Mw 7....
We provide a database of the coseismic geological surface effects following the Mw 6.5 Norcia earthquake that hit central Italy on 30 October 2016. This was one of the strongest seismic events to occur in Europe in the past thirty years, causing complex surface ruptures over an area of >400 km2. The database originated from the collaboration of sev...
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)...
To determine the importance of receiver fault geometry in Coulomb stress calculations a new methodology is presented to model faults with variable geometry. Although most models use planar faults, it is known that these are inaccurate representations of faults observed in the field. The central Italian Apennines are chosen as a straightforward tect...
We present a 1:25,000 scale map of the coseismic surface ruptures following the 30 October 2016 M w 6.5 Norcia normal-faulting earthquake, central Italy. Detailed rupture mapping is based on almost 11,000 oblique photographs taken from helicopter flights, that has been verified and integrated with field data (>7000 measurements). Thanks to the comm...
The temporal evolution of slip on surface ruptures during an earthquake is important for assessing fault displacement, defining seismic hazard and for predicting ground motion. However, measurements of near-field surface displacement at high temporal resolution are elusive. We present a novel record of near-field co-seismic displacement, measured w...
Whether slip-rates on active faults accumulated over multiple seismic events is constant or varying over tens to hundreds of millenia timescales is an open question that can be addressed through study of deformed Quaternary palaeoshorelines. It is important to know the answer so that one can judge whether shorter timescale measurements (e.g. Holoce...
Current studies of fault interaction lack sufficiently long earthquake records and measurements of fault slip-rates over multiple seismic cycles to fully investigate the effects of interseismic loading and co-seismic stress changes on the surrounding fault network. We model elastic interactions between 97 faults from 30 earthquakes since 1349 AD in...
In order to investigate the importance of including strike-variable geometry and the knowledge of historical and paleoseismic earthquakes when modelling static Coulomb stress transfer and rupture propagation, we have examined the August-October 2016 and January 2017 central Apennines seismic sequence (Mw 6.0, 5.9, 6.5 in 2016 (INGV) and Mw 5.1, 5.5...
Many areas of the Earth’s crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem...
Many areas of the Earth’s crust deform by distributed extensional faulting and the occurrence of earthquakes reflects complex fault interactions. Geodetic data may indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a...
We perform aftershock probabilistic seismic hazard analysis (APSHA) of the ongoing aftershock sequence following the Amatrice August 24th, 2016 Central Italy earthquake. APSHA is a time-dependent PSHA calculation where earthquake occurrence rates decrease after the occurrence of a mainshock following an Omori-type decay. In this paper we propose a...
Traditional seismic hazard assessment methods are based on the historical seismic records for the calculation of an annual probability of exceedance for a particular ground motion level. A new fault-specific seismic hazard assessment method is presented, in order to address problems related to the incompleteness and the inhomogeneity of the histori...
To determine the importance of receiver fault geometry in Coulomb stress calculations a new methodology is presented to model faults with variable geometry. Although most models use planar faults, it is known that these are inaccurate representations of faults observed in the field. The central Italian Apennines are chosen as a straightforward tect...
We present some preliminary results on the mapping of coseismically-induced ground ruptures following the Aug. 24, 2016, Central Italy earthquake (Mw 6.0). The seismogenic source, as highlighted by InSAR and seismological data, ruptured across two adjacent structures: the Vettore and Laga faults. We collected field data on ground breaks along the w...
In order to determine whether slip during an earthquake on the 26th September 1997 propagated to the surface, structural data have been collected along a bedrock fault scarp in Umbria, Italy. These collected data are used to investigate the relationship between the throw associated with a debated surface rupture (observed as a pale unweathered stri...
In order to determine whether slip during an earthquake on the 26th September 1997 propagated to the surface, structural data have been collected along a bedrock fault scarp in Umbria, Italy. These collected data are used to investigate the relationship between the throw associated with a debated surface rupture (observed as a pale unweathered stri...
This 2 days-long field trip aims at exploring field evidence of active tectonics, paleoseismology and Quaternary geology in the Fucino and L’Aquila intermountain basins and adjacent areas, within the inner sector of Central Apennines, characterized by extensional tectonics since at least 3 Ma. Each basin is the result of repeated strong earthquakes...
Long-term crustal extension rates, accommodated by active normal faults, can be constrained by investigating
Late Quaternary vertical movements. Sequences of marine terraces tectonically deformed by active faults mark the interaction between tectonic activity, sea-level changes and active faulting throughout the Quaternary (e.g. Armijo et al., 1996...
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 Fe...
Overview of combining regional strain-rate, slip-rate variability and stress transfer during fault interaction for seismic hazard assessment and understanding of continental deformation Abstract: Active faults experience earthquake rupture due to stress transfer from neighbouring earthquakes only if the fault in question is close to its failure str...
Strain-rates have been measured in the central Italian Apennines in a regular 5km and 20km square grids using field measurements of fault geometry, slip vectors and throw-rates measured across offset Late Pleistocene-Holocene landforms and sediments. Comparisons of these strain-rates with rates derived from historical seismicity and geodesy show th...
Study of the links between slip at depth and at the surface for the 1997 Colfiorito earthquakes using detailed structural mapping; the role of fault orientations. Abstract: Detailed structural mapping has been undertaken along fourteen different normal faults scarps throughout the central and northern Italian Apennines, including the Mt. Le Scalett...
We test interactions between sea-level change, climate and tectonic activity using a synchronous correlation method to refine and define ages of dated and undated Quaternary marine terraces sequences and their chronology. We mapped and measured the inner edge elevations of marine terraces, tectonically deformed by a Quaternary active normal fault,...
Due to its ~2 kyr “silent state”, the active Sulmona normal fault represents one of the most hazardous faults in central Italy, and the associated seismic risk is increased by the occurrence of important cities and several historical buildings and critical facilities. We investigated the central sector of the Sulmona fault through geological-geomor...
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...
Using combined datasets from ground penetrating radar (GPR) and terrestrial laser scanning (TLS) we document the variety of tectono-geomorphic features that contribute to the morphology of bedrock scarps associated with active extensional faulting in central Italy. Measurement of faulted offsets across such scarps can provide important fault slip-r...
Viscous flow in the deep crust and uppermost mantle can
contribute to the accumulation of strain along seismogenic
faults in the shallower crust1. It is difficult to evaluate
this contribution to fault loading because it is unclear
whether the viscous deformation occurs in localized shear
zones or is more broadly distributed2. Furthermore, the rate...