Preface: Linking faults to seismic hazard assessment in Europe

Martinelli, F.; Visini, Francesco; Scotti, Oona; Peruzza, Laura

doi:10.5194/nhess-18-1349-2018

“…Including fault maps in probabilistic seismic hazard analysis can overcome this problem (e.g. Chartier et al, ; Hodge et al, ; Pace et al, ), but this requires estimates of both earthquake magnitude and recurrence interval. In Lake Malawi, where fault slip rates have not been measured, Hodge et al () assigned the plate motion to individual faults in their hazard assessment.…”

Section: Discussionmentioning

confidence: 99%

Active Fault Scarps in Southern Malawi and Their Implications for the Distribution of Strain in Incipient Continental Rifts

Wedmore

¹

,

Biggs

²

,

Williams

³

et al. 2020

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The distribution of deformation during the early stages of continental rifting is an important constraint on our understanding of continental breakup. Incipient rifting in East Africa has been considered to be dominated by slip along rift border faults, with a subsequent transition to focused extension on axial segments in thinned crust and/or with active magmatism. Here, we study high-resolution satellite data of the Zomba Graben in southern Malawi, an amagmatic rift whose topography is dominated by the west-dipping Zomba fault. We document evidence for five subparallel fault scarps between 13 and 51 km long spaced~10-15 km apart. The scarps consist of up to five segments between 4 and 18 km long, separated by minima in scarp height and river knickpoints. The maximum height of each fault scarp ranges from 9.5 ± 4.2 m to 35.3 ± 14.6 m, with the highest scarp measured on the intrabasin Chingale Step fault. We estimate that the scarps were formed by multiple earthquakes of up to M w 7.1 and represent a previously unrecognized seismic hazard. Our calculations show that 55 ± 24% of extensional strain is accommodated across intrabasin faults within the~50 km wide rift. This demonstrates that a significant proportion of displacement can occur on intrabasin faults during early-stage rifting, even in thick continental lithosphere with no evidence for magmatic fluids.Plain Language Summary When continents begin to stretch, earthquakes occur on faults that incrementally accumulate slip to eventually form a rift valley. To estimate the hazard posed by these earthquakes, it is important to understand where these faults are located and how much stretching they each accommodate. We analyze faults in the Zomba Graben, a young rift in southern Malawi, using high-resolution satellite data. Steep scarps indicate that recent earthquakes have occurred at both the edges and in the middle of the rift valley. Pronounced activity in the rift middle is thought to require a thinned rigid outer layer of the Earth or mechanically unfavorable faults at the rift edge. Neither of these factors have been observed in southern Malawi. We suggest that the distribution of active faults, and hence of earthquakes, is likely controlled by weaknesses in the middle and lower parts of the Earth's crust.

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“…Presenting a new conceptual framework to gather fault data useful for SHA (seismic hazard assessment) was identified as a key challenge by the Fault2SHA Working Group ( http://fault2sha.net/ ) 1 , established within the European Seismological Commission (ESC) in 2016. To improve fault-based SHA, field geologists should provide the relevant observations, analysts should interpret field data appropriately 2 , and the full range of uncertainties associated with the characterization of faults should be correctly understood and propagated in computations 3 . To overcome the barriers that exist for the above, due to the different experience and expertise of participants, we, the Fault2SHA Central Apennines Laboratory, have brought together representatives from research groups across multiple institutions comprising field geologists, seismic hazard modellers and practitioners to create the Fault2SHA Central Apennines Database 4 .…”

Section: Background and Summarymentioning

confidence: 99%

“…Fault geometries and associated slip-rates are critical in determining earthquake locations and occurrence rates 2 , 3 , 5 in SHA: we acknowledge that including these data is key to improving earthquake hazard and risk estimates. Currently, most hazard models rely principally on historical earthquake rates, but these may not be representative of longer term rates (either overestimating or underestimating as typical recurrence intervals may be hundreds to many thousands of years yet historical records are rarely complete for more than a few hundred years), resulting in a bias in the probability and/or the potential magnitude of earthquakes (e.g.…”

Section: Background and Summarymentioning

confidence: 99%

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

Walker

¹

,

Boncio

²

,

Pace

³

et al. 2021

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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: 10.1594/PANGAEA.922582.

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“…Including fault maps in probabilistic seismic hazard analysis can overcome this problem (e.g. Chartier et al, 2017;Hodge et al, 2015;Pace et al, 2018), but this requires estimates of both earthquake magnitude and recurrence interval. In Lake Malawi, where fault slip rates have not been measured, Hodge et al (2015) assigned the plate motion to individual faults in their hazard assessment.…”

Section: Implications For Seismic Hazardmentioning

confidence: 99%

Active fault scarps in southern Malawi and their implications for the distribution of strain in incipient continental rifts

Wedmore¹,

Biggs²,

Williams³

et al. 2019

Preprint

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The distribution of deformation during the early stages of continental rifting is an important constraint on our understanding of continental breakup. Incipient rifting in East Africa has been considered to be dominated by slip along rift border faults, with a subsequent transition to focussed extension on axial segments in thinned crust and/or with active magmatism. Here, we study high-resolution satellite data of the Zomba Graben in southern Malawi, an amagmatic rift whose topography is dominated by the west-dipping Zomba fault. We document evidence for five sub-parallel fault scarps between 13 and 51 km long spaced ~10-15 km apart. The scarps consist of up to five segments between 4-18 km long, separated by minima in scarp height and river knickpoints. The maximum height of each fault scarp ranges from 9.5 ± 4.2 m to 35.3 ± 14.6 m, with the highest scarp measured on the intrabasin Chingale Step fault. We estimate that the scarps were formed by multiple earthquakes of up to Mw7.1, and represent a previously unrecognized seismic hazard. Our calculations show that 55 ± 24 % of extensional strain is accommodated across intrabasin faults within the ~50 km wide rift. This demonstrates that a significant proportion of displacement can occur on intrabasin faults during early stage rifting, even in thick continental lithosphere with no evidence for magmatic fluids.

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Preface: Linking faults to seismic hazard assessment in Europe

Cited by 7 publications

References 12 publications

Active Fault Scarps in Southern Malawi and Their Implications for the Distribution of Strain in Incipient Continental Rifts

Active Fault Scarps in Southern Malawi and Their Implications for the Distribution of Strain in Incipient Continental Rifts

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

Active fault scarps in southern Malawi and their implications for the distribution of strain in incipient continental rifts

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