Spatiotemporal Dynamics of Clusters in the Bridge Zone Linking L'Aquila 2009 and Central Italy 2016 Seismic Sequences
DOI:
https://doi.org/10.26443/seismica.v5i1.1676Keywords:
Seismicity, Clusters, Campotosto Seismic zone, Spatiotemporal dynamicsAbstract
We analyze the spatiotemporal evolution of earthquake clusters in the Campotosto area, located between the L'Aquila 2009 and Central Italy 2016 seismic sequences. This region has experienced several moderate earthquakes (Mw 5–5.5) and persistent low-level seismicity. Using a hierarchical density-based algorithm on high-resolution catalogs, we identify clusters lasting from days to months and migrating at rates of meters to kilometers per day. These clusters alternate between phases of rapid expansion and slower diffusion, reflecting complex interactions among fluids, aseismic slip, and seismic rupture across fault segments. Energy release within clusters is low, with effective stress drop ranging from 0.01 to 1 MPa, suggesting diverse driving processes. Clusters with larger spatial extents tend to exhibit lower effective stress drop, implying a significant aseismic slip component, consistent with remote sensing observations. Our findings indicate that deep fluids promote multiphase slip and fault reactivation, influencing seismicity across fault segments with varying criticality. Variations in fault orientation and dip further contribute to heterogeneous slip distribution, affecting both energy release and cluster formation.
References
Abercrombie, R. E. (1995). Earthquake source scaling relationships from -1 to 5 ML using seismograms recorded at 2.5 km depth. Journal of Geophysical Research: Solid Earth, 100(B12), 24015–24036. https://doi.org/10.1029/95JB02397
Artale Harris, P., Scognamiglio, L., Magnoni, F., Casarotti, E., & Tinti, E. (2022). Centroid moment tensor catalog with 3D lithospheric wave speed model: The 2016–2017 Central Apennines sequence. Journal of Geophysical Research: Solid Earth, 127:e2021JB023068. https://doi.org/10.1029/2021JB023068
Barchi, M. R., Carboni, F., Michele, M., Ercoli, M., Giorgetti, C., Porreca, M., & others. (2021). The influence of subsurface geology on the distribution of earthquakes during the 2016–2017 Central Italy seismic sequence. Tectonophysics, 807, 228797. https://doi.org/10.1016/j.tecto.2021.228797
Bigi, S., Casero, P., Chiarabba, C., & Di Bucci, D. (2013). Contrasting surface active faults and deep seismogenic sources unveiled by the 2009 L’Aquila earthquake sequence (Italy). Terra Nova, 25(1), 21–29. https://doi.org/10.1111/ter.12000
Bradford Barber, C., Dobkin, D. P., & Huhdanpaa, H. (1996). The Quickhull algorithm for convex hulls. ACM Trans. Math. Softw., 22(4), 469–483. https://doi.org/10.1145/235815.235821
Brennan Brunsvik, G., Morra, G., Cambiotti, G., Chiaraluce, L., Di Stefano, R., De Gori, P., & Yuen, D. A. (2021). Three-dimensional Paganica fault morphology obtained from hypocenter clustering (L’Aquila 2009 seismic sequence, Central Italy). Tectonophysics, 804. https://doi.org/10.1016/j.tecto.2021.228756
Buttinelli, M., Petracchini, L., Maesano, F. E., D’Ambrogi, C., Scrocca, D., Marino, M., Capotorti, F., Bigi, S., Cavinato, G. P., Mariucci, M. T., Montone, P., & Di Bucci, D. (2021). The impact of structural complexity, fault segmentation, and reactivation on seismotectonics: Constraints from the upper crust of the 2016–2017 Central Italy seismic sequence area. Tectonophysics, 810. https://doi.org/10.1016/j.tecto.2021.228861
Calderoni, G., & Abercrombie, R. (2023). Investigating spectral estimates of stress drop for small to moderate earthquakes with heterogeneous slip distribution: Examples from the 2016–2017 Amatrice earthquake sequence. Journal of Geophysical Research, 128(6). https://doi.org/10.1029/2022jb025022
Calderoni, G., Rovelli, A., & Di Giovambattista, R. (2017). Rupture directivity of the strongest 2016–2017 central Italy earthquakes. Journal of Geophysical Research: Solid Earth, 122, 9118–9131. https://doi.org/10.1002/2017JB014118
Campello, R. J. G. B., Moulavi, D., & Sander, J. (2013). Density-based clustering based on hierarchical density estimates. Pacific-Asia Conference on Knowledge Discovery and Data Mining . Springer, 160–172. https://doi.org/10.1007/978-3-642-37456-2_14
Campello, R. J. G. B., Moulavi, D., Zimek, A., & Sander, J. (2015). Hierarchical density estimates for data clustering, visualization, and outlier detection. ACM Transactions on Knowledge Discovery from Data (TKDD), 10(1), 1–51. https://doi.org/10.1145/2733381
Carpenter, B. M., Scuderi, M. M., Collettini, C., & Marone, C. (2014). Frictional heterogeneities on carbonate-bearing normal faults: Insights from the Monte Maggio Fault, Italy. Journal of Geophysical Research: Solid Earth, 119. https://doi.org/10.1002/2014JB011337
Cheloni, D., D’Agostino, N., Scognamiglio, L., & others. (2019). Heterogeneous behavior of the Campotosto normal fault (Central Italy) imaged by InSAR GPS and strong-motion data: Insights from the 18 January 2017 events. Remote Sensing, 11(12), 1482. https://doi.org/10.3390/rs11121482
Chiarabba, C., De Gori, P., Cattaneo, M., & others. (2018). Faults geometry and the role of fluids in the 2016–2017 Central Italy seismic sequence. Geophysical Research Letters, 45(14), 6963–6971. https://doi.org/10.1029/2018gl077485
Chiaraluce, L., Di Stefano, R., Tinti, E., Scognamiglio, L., Michele, M., Casarotti, E., Cattaneo, M., De Gori, P., Chiarabba, C., Monachesi, G., Lombardi, A., Valoroso, L., Latorre, D., & Marzorati, S. T. (2017). Central Italy Seismic Sequence: A First Look at the Mainshocks, Aftershocks, and Source Models. Seismological Research Letters, 88(3), 757–771. https://doi.org/10.1785/0220160221
Chiaraluce, L., Ellsworth, W. L., Chiarabba, C., & Cocco, M. (2003). Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study. Journal of Geophysical Research, 108(B6), 2294. https://doi.org/10.1029/2002JB002166
Chiaraluce, L., Michele, M., Waldhauser, F., & others. (2022). A comprehensive suite of earthquake catalogues for the 2016–2017 Central Italy seismic sequence. Scientific Data, 9(1). https://doi.org/10.1038/s41597-022-01827-z
Chiaraluce, L., Valoroso, L., Piccinini, D., Di Stefano, R., & De Gori, P. (2011). The anatomy of the 2009 L’Aquila normal fault system (central Italy) imaged by high resolution foreshock and aftershock locations. Journal of Geophysical Research: Solid Earth, 116(B12). https://doi.org/10.1029/2011JB008352
Cirella, A., Piatanesi, A., Cocco, M., Tinti, E., Scognamiglio, L., Michelini, A., Lomax, A., & Boschi, E. (2009). Rupture history of the 2009 L’Aquila (Italy) earthquake from non-linear joint inversion of strong motion and GPS data. Geophysical Research Letters, 36, L19304. https://doi.org/10.1029/2009GL039795
Civico, R., Blumetti, A. M., Chiarini, E., Cinti, F. R., La Posta, E., Papasodaro, F., Sapia, V., Baldo, M., Lollino, G., & Pantosti, D. (2016). Traces of the active Capitignano and San Giovanni faults (Abruzzi Apennines, Italy). Journal of Maps, 12(sup1), 453–459. https://doi.org/10.1080/17445647.2016.1239229
Collettini, C., & Tinti, E. (2025). The influence of lithology and fault source volume on the magnitude–frequency distribution of earthquakes. Geophysical Research Letters, 52. https://doi.org/10.1029/2024GL110354
Danecek, P., Pintore, S., Mazza, S., Mandiello, A., Fares, M., Carluccio, I., Della Bina, E., Franceschi, D., Moretti, M., Lauciani, V., Quintiliani, M., & Michelini, A. (2021). The Italian Node of the European Integrated Data Archive. Seismological Research Letters, 92(3), 1726–1737. https://doi.org/10.1785/0220200409
de Berg, M., Gunawan, A., & Roeloffzen, M. (2017). Faster DBScan and HDBScan in Low-Dimensional Euclidean Spaces. International Symposium on Algorithms and Computation. https://doi.org/10.4230/LIPICS.ISAAC.2017.25
De Gori, P., Michele, M., Chiaraluce, L., & Chiarabba, C. (2023). Fault rheology control on rupture propagation and aftershocks distribution during the 2016–2017 Central Italy earthquakes. Seismological Research Letters, 94(6), 2642–2654. https://doi.org/10.1785/0220220284
Essing, D., & Poli, P. (2024). Unraveling earthquake clusters composing the 2014 Alto Tiberina earthquake swarm via unsupervised learning. Journal of Geophysical Research: Solid Earth. https://doi.org/10.1029/2022JB026237
Ester, M., Kriegel, H.-P., Sander, J., & Xu, X. (1996). A density-based algorithm for discovering clusters in large spatial databases with noise. Proceedings of the Second International Conference on Knowledge Discovery and Data Mining, 226–231. https://doi.org/10.5555/3001460.3001507
Falcucci, E., Gori, S., Bignami, C., Pietrantonio, G., Melini, D., Moro, M., Saroli, M., & Galadini, F. (2018). The Campotosto seismic gap in between the 2009 and 2016–2017 seismic sequences of central Italy and the role of inherited lithospheric faults in regional seismotectonic settings. Tectonics, 37, 2425–2445. https://doi.org/10.1029/2017TC004844
Faure Walker, J. P., Boncio, P. B., Roberts, G. P., Benedetti, L., Scotti, O., Visini, F., & Peruzza, L. (2021). Fault2SHA Central Apennines database and structuring active fault data for seismic hazard assessment. Scientific Data, 8(1), 87. https://doi.org/10.1038/s41597-021-00868-0
Fischer, T., & Hainzl, S. (2017). Effective Stress Drop of Earthquake Clusters. Bulletin of the Seismological Society of America, 107(5), 2247–2257. https://doi.org/ 10.1785/0120170035
Fischer, T., & Hainzl, S. (2021). The Growth of Earthquake Clusters. Frontiers in Earth Science, 9. https://doi.org/10.3389/feart.2021.638336
Gualandi, A., Serpelloni, E., & Belardinelli, M. E. (2014). Space–time evolution of crustal deformation related to the Mw 6.3, 2009 L’Aquila earthquake (central Italy) from principal component analysis inversion of GPS position time-series. Geophysical Journal International, 197(1), 174–191. https://doi.org/10.1093/gji/ggt522
Hainzl, S. (2004). Seismicity patterns of earthquake swarms due to fluid intrusion and stress triggering. Geophysical Journal International, 159(3), 1090–1096. https://doi.org/10.1111/j.1365-246X.2004.02463.x
Hainzl, S., Fischer, T., & Dahm, T. (2012). Seismicity-based estimation of the driving fluid pressure in the case of swarm activity in Western Bohemia. Geophysical Journal International, 191(1), 271–281. https://doi.org/10.1111/j.1365-246X.2012.05610.x
Hunt, E. L., & Reffert, S. (2021). Improving the open cluster census. Astronomy and Astrophysics, 646, A104. https://doi.org/10.1051/0004-6361/202039341
Lavecchia, G., Bello, S., Andrenacci, C., Cirillo, D., Ferrarini, F., Vicentini, N., de Nardis, R., & Brozzetti, F. (2021). QUaternary fault strain INdicators database: QUIN 1.0 - first release from the Apennines of central Italy. PANGAEA. https://doi.org/10.1594/PANGAEA.934802
Lee, J., Tsai, V. C., Chatterjee, A., & Trugman, D. T. (2024). Fault-network geometry influences earthquake frictional behaviour. Nature, 631(106), 110. https://doi.org/10.1038/s41586-024-07518-6
Lelis, L., & Sander, J. (2009). Semi-supervised density-based clustering. IEEE 9th International Conference on Data Mining, 842–847. https://doi.org/10.1109/ICDM.2009.143
Locchi, M. E., Scognamiglio, L., Tinti, E., & Collettini, C. (2024). A large fault partially reactivated during two contiguous seismic sequences in Central Italy: The role of geometrical and frictional heterogeneities. Tectonophysics, 877, 230284. https://doi.org/10.1016/j.tecto.2024.230284
Lomax, A., Virieux, J., Volant, P., & Berge-Thierry, C. (2000). Probabilistic earthquake location in 3D and layered models. In C. H. Thurber & N. Rabinowitz (Eds.), Advances in Seismic Event Location. Modern Approaches in Geophysics, 18. Springer. https://doi.org/10.1007/978-94-015-9536-0_5
Ma, B., Yang, C., Li, A., Chi, Y., & Chen, L. (2023). A Faster DBSCAN Algorithm Based on Self-Adaptive Determination of Parameters. Procedia Computer Science, 221, 113–120. https://doi.org/10.1016/j.procs.2023.07.017
Magnoni, F., Casarotti, E., Komatitsch, D., & others. (2022). Adjoint tomography of the Italian lithosphere. Communications Earth and Environment, 3, 69. https://doi.org/10.1038/s43247-022-00397-7
Malagnini, L., Lucente, F. P., De Gori, P., Akinci, A., & Munafo’, I. (2012). Control of pore fluid pressure diffusion on fault failure mode: Insights from the 2009 L’Aquila seismic sequence. Journal of Geophysical Research, 117, B05302. https://doi.org/10.1029/2011JB008911
Malagnini, L., & Munafò, I. (2018). On the Relationship between MwMw and M0M0 in a Broad Range: An Example from the Apennines, Italy. Bulletin of the Seismological Society of America, 108(2), 1018–1024. https://doi.org/10.1785/0120170303
Malagnini, L., Nielsen, S., Mayeda, K., & Boschi, E. (2010). Energy radiation from intermediate- to large-magnitude earthquakes: Implications for dynamic fault weakening. Journal of Geophysical Research, 115, B06319. https://doi.org/10.1029/2009JB006786
Mancini, S., Segou, M., Werner, M. J., Parsons, T., Beroza, G., & Chiaraluce, L. (2022). On the use of high-resolution and deep-learning seismic catalogs for short-term earthquake forecasts: Potential benefits and current limitations. Journal of Geophysical Research: Solid Earth, 127, e2022JB025202. https://doi.org/10.1029/2022JB025202
Mandler, E., Pintori, F., Gualandi, A., Anderlini, L., Serpelloni, E., & Belardinelli, M. E. (2021). Post-seismic deformation related to the 2016 Central Italy seismic sequence from GPS displacement time-series. Journal of Geophysical Research: Solid Earth, 126, e2021JB022200. https://doi.org/10.1029/2021JB022200
Moratto, L., Santulin, M., Tamaro, A., & others. (2023). Near-source ground motion estimation for assessing the seismic hazard of critical facilities in central Italy. Bulletin of Earthquake Engineering, 21, 53–75. https://doi.org/10.1007/s10518-022-01555-0
Moutote, L., Itoh, Y., Lengliné, O., Duputel, Z., & Socquet, A. (2023). Evidence of a transient aseismic slip driving the 2017 Valparaiso earthquake sequence, from foreshocks to aftershocks. Journal of Geophysical Research: Solid Earth, 128: e2023JB026603. https://doi.org/10.1029/2023JB026603
Peng, Z., & Lei, X. (2025). Physical mechanisms of earthquake nucleation and foreshocks: Cascade triggering, aseismic slip, or fluid flows? Earthquake Research Advances, 5(2), 100349. https://doi.org/10.1016/j.eqrea.2024.100349
Perfettini, H., Schmittbuhl, J., & Cochard, A. (2003). Shear and normal load perturbations on a two-dimensional continuous fault: 1. Static triggering. Journal of Geophysical Research: Solid Earth, 108(B9). https://doi.org/10.1029/2002JB001804
Piana Agostinetti, N., Giacomuzzi, G., & Chiarabba, C. (2017). Seismic swarms and diffuse fracturing within Triassic evaporites fed by deep degassing along the low-angle Alto Tiberina normal fault (central Apennines, Italy). Journal of Geophysical Research: Solid Earth, 122(1), 308–331. https://doi.org/10.1002/2016JB013295
Piegari, E., Camanni, G., Mercurio, M., & Marzocchi, W. (2024). Illuminating the hierarchical segmentation of faults through an Unsupervised Learning Approach applied to clouds of earthquake hypocenters. Earth and Space Science, 11:e2023EA003267. https://doi.org/10.1029/2023EA003267
Pino, N. A., Convertito, V., & Madariaga, R. (2019). Clock advance and magnitude limitation through fault interaction: The case of the 2016 central Italy earthquake sequence. Scientific Reports, 9(1), 5005–5005. https://doi.org/10.1038/s41598-019-41453-1
Pizzi, A., Di Domenica, A., Galluzzo, F., & Innocenti, C. (2017). Fault segmentation as constraint to the occurrence of the main shocks of the 2016 Central Italy seismic sequence. Tectonics, 36(12). https://doi.org/10.1002/2017TC004652
Roche, V., van der Baan, M., & Walsh, J. (2025). The role of the three-dimensional geometry of fault steps on event migration during fluid-induced seismic sequences. Journal of Geophysical Research: Solid Earth, 130: e2024JB029476. https://doi.org/10.1029/2024JB029476
Roland, E., & McGuire, J. J. (2009). Earthquake swarms on transform faults. Geophysical Journal International, 178(3), 1677–1690. https://doi.org/10.1111/j.1365-246X.2009.04214.x
Rousseeuw, P. J. (1987). Silhouettes: a Graphical Aid to the Interpretation and Validation of Cluster Analysis. Computational and Applied Mathematics, 20, 53–65. https://doi.org/10.1016/0377-0427(87)90125-7
Schoenball, M., & Ellsworth, W. L. (2017). A systematic assessment of the spatiotemporal evolution of fault activation through induced seismicity in Oklahoma and Southern Kansas. Journal of Geophysical Research: Solid Earth, 122(12), 10189–10206. https://doi.org/10.1002/2017JB014850
Shapiro, S. A., & Dinske, C. (2009). Scaling of seismicity induced by nonlinear fluid-rock interaction. Geophysical Research Letters, 36, L18302. https://doi.org/10.1029/2009GL039500
Shapiro, S. A., Huenges, E., & Borm, G. (1997). Estimating the crust permeability from fluid-injection-induced seismic emission at the KTB site. Geophysical Journal International, 131(2), 15–18. https://doi.org/10.1111/j.1365-246X.1997.tb01215.x
Soldati, G., Zaccarelli, L., & Faenza, L. (2019). Spatio-temporal seismic velocity variations associated to the 2016–2017 central Italy seismic sequence from noise cross-correlation. Geophysical Journal International, 219(3), 2165–2173. https://doi.org/10.1093/gji/ggz429
Spallarossa, D., Picozzi, M., Scafidi, D., Morasca, P., Turino, C., & Bindi, D. (2021). The RAMONES Service for Rapid Assessment of Seismic Moment and Radiated Energy in Central Italy: Concepts, Capabilities, and Future Perspectives. Seismological Research Letters, 92(3), 1759–1772. https://doi.org/10.1785/0220200348
Sugan, M., Campanella, S., Chiaraluce, L., Michele, M., & Vuan, A. (2023). The unlocking process leading to the 2016 Central Italy seismic sequence. Geophysical Research Letters, 50:e2022GL101838. https://doi.org/10.1029/2022GL101838
Sugan, M., Kato, A., Miyake, H., Nakagawa, S., & Vuan, A. (2014). The preparatory phase of the 2009 Mw6.3 L’Aquila earthquake by improving the detection capability of low-magnitude foreshocks. Geophysical Research Letters, 41, 6137–6144. https://doi.org/10.1002/2014GL061199
Tan, Y. J., Waldhauser, F., Ellsworth, W. L., Zhang, M., Zhu, W., Michele, M., Chiaraluce, L., Beroza, G. C., & Segou, M. (2021). Machine-Learning-Based High-Resolution Earthquake Catalog Reveals How Complex Fault Structures Were Activated during the 2016–2017 Central Italy Sequence. The Seismic Record, 1(1), 11–19. https://doi.org/10.1785/0320210001
Tinti, E., Scognamiglio, L., Michelini, A., & Cocco, M. (2016). Slip heterogeneity and directivity of the ML 6.0, 2016, Amatrice earthquake estimated with rapid finite-fault inversion. Geophysical Research Letters, 43(10), 745–10. https://doi.org/10.1002/2016GL071263
Tondi, E., Jablonska, D., Volatili, T., Michele, M., & others. (2020). The Campotosto linkage fault zone between the 2009 and 2016 seismic sequences of central Italy: Implications for seismic hazard analysis. Geological Society of America Bulletin, 133, 1679–1694. https://doi.org/10.1130/b35788.1
Valoroso, L., Chiaraluce, L., Piccinini, D., Di Stefano, R., Schaff, D., & Waldhauser, F. (2013). Radiography of a normal fault system by 64,000 high-precision earthquake locations: The 2009 L’Aquila (central Italy) case study. Journal of Geophysical Research: Solid Earth, 118, 1156–1176. https://doi.org/10.1002/jgrb.50130
Vičič, B., Aoudia, A., Borghi, A., Momeni, S., & Vuan, A. (2020). Seismicity rate changes and geodetic transients in Central Apennines. Geophysical Research Letters, 47:e2020GL090668. https://doi.org/10.1029/2020GL090668
Vuan, A., Sugan, M., Chiaraluce, L., & Di Stefano, R. (2017). Loading rate variations along a midcrustal shear zone preceding the Mw6.0 earthquake of 24 August 2016 in Central Italy. Geophysical Research Letters, 44(12), 170–12. https://doi.org/10.1002/2017GL076223
Waldhauser, F., & Ellsworth, W. L. (2000). A double-difference earthquake location algorithm: Method and application to the northern Hayward fault. Bull. Seism. Soc. Am., 90, 1353–1368. https://doi.org/10.1785/0120000006
Waldhauser, F., Michele, M., Chiaraluce, L., Di Stefano, R., & Schaff, D. P. (2021). Fault planes, fault zone structure and detachment fragmentation resolved with high-precision aftershock locations of the 2016–2017 Central Italy sequence. Geophysical Research Letters, 48(16). https://doi.org/10.1029/2021GL092918
Ward, J. H. (1963). Hierarchical grouping to optimize an objective function. Journal of the American Statistical Association, 58(301), 236–244. https://doi.org/10.1080/01621459.1963.10500845
Zhang, Q., & Shearer, P. M. (2016). A new method to identify earthquake swarms applied to seismicity near the San Jacinto Fault, California. Geophysical Journal International, 205(2), 995–1005. https://doi.org/10.1093/gji/ggw073
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