Linking surface deformation with lower crustal shear zones: insights into drivers of millennial-scale earthquake clustering and time-dependent seismic hazard
- 1School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK. (zoe.mildon@plymouth.ac.uk)
- 2Department of Earth and Planetary Sciences, Birkbeck, University of London, London WC1E 7HX, UK
- 3Institute of Risk and Disaster Reduction, University College London, Gower Street, London WC1E 6BT, UK
- 4Computer, Electrical and Mathematical Sciences and Engineering, 4700 King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Kingdomof Saudi Arabia.
- 5Laboratory of Mineralogy and Geology, Department of Natural Resources Development & Agricultural Engineering, Agricultural University of Athens, 11855 Athens, Greece
- 6Dipartimento di Scienza ed Alta Tecnologia, Università degli Studi dell’Insubria, Como, Italy
- 7Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli Osservatorio Vesuviano, Via Diocleziano 328, 80124 Naples, Italy
- 8International Research Institute of Disaster Science, Tohoku University, Sendai, Japan
- 9DiSTAR—Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, University ofNaples “Federico II”, Naples, Italy.
- 10School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK
- 11Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK
- 12Scottish Universities Environmental ResearchCentre,GlasgowG75 0QF, UK
- 13Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa, 153, 90146 Palermo, Italy
- 14CNR, Institute of Geosciences and Earth Resources, Via La Pira 4, 50121 Florence, Italy.
Surface faulting earthquakes are known to cluster in time from historical and palaeoseismic studies in multiple active tectonic settings, including central Greece, southern California and central Italy. However, 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 combine surface dating of active normal fault scarps in central Italy with stress modelling and quartz flow laws, to produce a quantified replication of observed earthquake clustering.
We study six active normal faults (including the Mt Vettore fault which ruptured during the 2016 central Italy earthquake sequence) using 36Cl cosmogenic dating. This reveals periods of high and low slip rate, which we interpret to be earthquake clusters/anti-clusters. Interestingly, these changes in slip rate (or clustering) are out-of-phase between neighbouring faults, i.e. when one fault slows down, nearby faults speed up at the same time. To explore the underlying processes driving this out-of-phase clustering behaviour, we link stress transfer caused by slip over clusters/anti-clusters on coupled fault/shear-zone structures with viscous quartz flow laws derived from laboratory experiments.
We show that differential stress fluctuates due to fault/shear-zone interactions, and that the magnitude of these fluctuations are sufficient to induce changes in strain-rate and associated slip-rate on neighbouring faults and shear zones. Our results suggest that fault/shear-zone interactions are a plausible and quantifiable explanation for earthquake clustering, thus opening possibilities for process-led and time-dependent seismic hazard assessments.
How to cite: Mildon, Z., Roberts, G., Faure Walker, J., Beck, J., Papanikolaou, I., Michetti, A., Toda, S., Iezzi, F., Campbell, L., McCaffrey, K., Shanks, R., Sgambato, C., Robertson, J., Meschis, M., and Vittori, E.: Linking surface deformation with lower crustal shear zones: insights into drivers of millennial-scale earthquake clustering and time-dependent seismic hazard, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15260, https://doi.org/10.5194/egusphere-egu23-15260, 2023.
