Abstract
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, 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.
The Dead Sea Fault (DSF) is a plate‐boundary where large earthquakes are expected, but there is a lack of such events in the instrumental era. Sequences of earthquakes along the DSF are documented by ...historical evidence, one of the most devastating occurred in the mid‐eighth century CE. Here we describe site‐specific archaeoseismological observations at the ancient Tiberias city, on the western shore of the Sea of Galilee. We map Roman and Byzantine relics faulted in the mid‐eighth century CE by a pure normal fault. We use geophysical, geomorphological, and structural analyses integrated with published data, to assess the seismic hazard of the Jordan Valley Western Boundary Fault (JVWB). We propose that the normal JVWB can rupture the surface along its ~45 km trace running from Tiberias toward the S crossing Bet Shean, Tel Rehov, and Tel Teomim. The JVWB, parallel to the main strike‐slip Jordan Valley Fault segment, might be regarded as a major earthquake source in this region. We test the hypotheses of both single fault and multifaults rupture scenarios, which result in an expected range of Mw from 6.9 (single rupture of the JVWB) to 7.6 (multiple rupture of the JVWB and Jordan Valley Fault). Our results suggest that seismic source characterization in the Sea of Galilee region must include normal faults capable of surface rupturing, despite the absence of such events in the instrumental catalogue.
Key Points
Surface faulting affected the archeological relics at the ancient Tiberias (Dead Sea Fault, Israel)
We attribute this faulting to a mid‐eighth century CE earthquake
Our findings highlight the need for revising the tectonic setting and seismic risk in the Sea of Galilee and nearby regions
In the period of October–December 2019, the Cotabato–Davao del Sur region (Philippines) was hit by a seismic sequence comprising four earthquakes with magnitude
M
W
> 6.0 (EQ1-4; max magnitude
M
W
...6.8). The earthquakes triggered widespread environmental effects, including landslides and liquefaction features. We documented such effects by means of field surveys, which we supplemented with landslide mapping from satellite images. Field surveys allowed us to gather information on 43 points after EQ1, 202 points after EQs2–3 and 87 points after EQ4. Additionally, we built a multi-temporal inventory of landslides from remote sensing, comprising 190 slope movements triggered by EQ1, 4737 after EQs2–3, and 5666 at the end of the sequence. We assigned an intensity value to each environmental effect using the environmental seismic intensity (ESI-07) scale. Our preferred estimates of ESI-07 epicentral intensity are VIII for the first earthquake and IX at the end of the sequence, which is in broad agreement with other events of similar magnitude globally. This study, which is the first case of the application of the ESI-07 scale to a seismic sequence in the Philippines, shows that repeated documentation of environmental damage and the evaluation of the progression through time may be useful for providing input data for derivative products, such as susceptibility assessment, evaluation of residual risk or investigation of the role played by ground shaking and by other mechanisms able to trigger environmental effects.
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 in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic
Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The
Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (10
yr; 10
km) but over shorter timescales most of the deformation may be accommodated by <30% of the across-strike fault array. We attribute the shifts in activity to temporal variations in the mechanical work of faulting.
On 6 April 2009, a moderate earthquake (Mw = 6.3; Ml = 5.8) struck the Abruzzo region in central Italy, causing more than 300 fatalities and heavy damage to L'Aquila and surrounding villages. ...Coseismic surface effects have been thoroughly documented by timely field surveys as well as by remote sensing analyses of satellite images. The outstanding quality of geological, seismological, geodetic, and interferometric synthetic aperture radar (InSAR) information arguably represents the best ever data set made available immediately after a moderate seismic event. Based on this data set, we aim at testing the capability of coupled geological and InSAR data to map surface faulting patterns associated with moderate earthquakes. Coseismic ground ruptures have been mapped at a scale of 1:500 in the whole epicentral area. Traces of surface ruptures have been inferred from linear phase discontinuities identified in the interferogram. A very good agreement between the two methods resulted in the characterization of the main surface rupture along the Paganica fault. The same approach applied to ground ruptures hypothesized along other capable fault segments provided more questionable results. Thus, the combined field and InSAR approach appeared useful for detecting continuous surface ruptures exceeding 1 km in length and showing displacements greater than a few centimeters. These are the typical faulting parameters for moderate earthquakes (6.0 < Mw < 6.5) in central Apennines. For continuous ground cracks shorter than a few hundred meters and/or that show displacements smaller than 1–2 cm, the described approach may be less helpful, most probably due to the limited resolution of the data.
To 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±3ka 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±3ka (0.4–3.1mm/yr along 90km transects) occur in two areas (Lazio-Abruzzo; SE Campania and Basilicata) where values for finite extensional strains that have developed since 2–3Ma are highest (2–7km cumulative throw), and where mean elevation in 5×90km NE–SW boxes is >600m; the intervening area (NW Campania and Molise) with<600m mean elevation in 5×90km boxes has extension-rates<0.4mm/yr and lower values for finite extensional strains (<2km cumulative throw). These two areas with high upper-crustal strain-rates overlie mantle that has relatively-long spatially-interpolated SKS delay times (1.2–1.8s) indicating relatively-high mantle strains and free-air gravity values (140–160mGals); the intervening area of lower extension-rate has shorter spatially-interpolated SKS delay times (0.8–1.2s) and lower free-air gravity values (120mGals). 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.
► A strain-rate field is calculated from offset across 15ka fault scarps. ► Strain-rates correlate with slab window mantle tomography. ► Strain rates in the upper crust may be controlled by mantle strain-rates.
The historical center of Como (Northern Italy) is prone to lake flooding and subsidence, due to the presence of unconsolidated silty sediments with poor mechanical properties. The sedimentary basin ...beneath the town contains over 180m thickness of Late-Quaternary lacustrine, palustrine and alluvial deposits. The landscape evolution and the present-day environmental setting of the Como area have been reconstructed based on (i)more than 250 core logs and related geotechnical tests, (ii) detailed stratigraphic, sedimentological, paleobotanical and geotechnical analysis of several key boreholes, (iii) multi-year hydrogeological monitoring, (iv) estimation of subsidence rates and (v)integration of geomorphology, archeological findings and historical documents.
Based on our environmental analysis, we derived an integrated geological and geomorphological model of the latest Pleistocene to Holocene local landscape evolution. This model was used to help design an engineering facility to mitigate flood hazards in the Como urban area.
In 2012, we carried out investigations during a re-evaluation of the design parameters for the flood mitigation project at the Como lake-shore. The new campaign included seven boreholes, many in situ and laboratory tests, and four 14C dates. We found an organic silty unit, historical in age, with bad mechanical properties that was critical in the design of the flood mitigation project. We also obtained index properties for static and dynamic conditions, necessary for robust engineering planning. The results were used to update the project and better define future executive phases. Although the importance of acquiring independent experimental data is often overlooked, they can significantly improve the reliability of engineered systems, as demonstrated by the Como town case history.
•Como is affected by subsidence because it is built on compressible sediments.•Our multidisciplinary study reconstructed the recent landscape evolution around Como.•Our engineering geological model was used in a project for mitigating flood hazard.•This approach provided a predictive tool for risk management and urban planning.
The September–October 1997 seismic sequence in the Umbria–Marche regions of Central Italy has been one of the best studied from the seismological, macroseismic and geological point of view.
Numerous ...papers have been published in the period immediately after the seismic sequence, providing a significant database of effects triggered by the earthquake on natural environment.
In the following years, further studies have provided additional pieces of evidence that allow to better relate the seismic sequence with its geological background. Moreover, recent developments in the characterization of coseismic environmental effects provide new horizons in seismic hazard assessment (SHA) procedures, which should take into account even long term geomorphological and geological features resulting from repeated characteristic earthquakes (concept of “seismic landscape”).
This paper reviews the current state of knowledge on the 1997 Umbria–Marche seismic sequence, with particular regard to coseismic environmental effects (primary and secondary), that have been used for ESI seismic intensity assessment, in order to verify if i) they are consistent with geological, seismological and macroseismic data in the location and characterization of the seismogenic structure, and ii) if they fit the “seismic landscape” features that mark the epicentral area of Colfiorito.
SUMMARY
We captured post‐seismic deformation close to the surface rupture of the 2009 L’Aquila earthquake (M6.3, central Italy) using repeat terrestrial laser scan (TLS) methods. From 8 to 126 d ...after the earthquake, we repeatedly laser scanned four road surfaces that intersected the earthquake surface rupture. We modelled vertical near‐field deformation, at millimetre‐level precision, by comparing subsequent laser scan data sets to the first acquired at each site. The horizontal post‐seismic deformation at each site was measured between reflectors paired across the rupture. The TLS data were supplemented by total station data from a fifth site which measured the vertical and horizontal components of post‐seismic deformation between two points spanning the rupture. We find post‐seismic deformation increased between 44 and 126 d at the southeastern end of the rupture, beneath which a significant gradient in coseismic slip exists within the fault zone. The location, rate of decay and spatially‐localized nature of the post‐seismic deformation, within tens of metres of the surface rupture suggests it is due to afterslip in the fault zone, driven by increased shear stresses at the edges of regions which slipped coseismically. We note that the magnitude of post‐seismic deformation in the far field obtained from InSAR and GPS is not significantly greater than the deformations we have measured close to the rupture. We suggest that shallow, localized afterslip within the fault zone is responsible for the majority of the regional post‐seismic deformation field.
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