A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas
Estimating Earthquake Magnitude of Seismogenic Sources
This section illustrates the criteria and methods adopted to estimate the magnitude associated with the seismogenic sources in DISS v. 3.3.0 (DISS Working Group, 2021). The methodology adopted here for the CSS and SDS is an update of what was already adopted for studies of earthquake hazards where the DISS was used as an input dataset (Basili et al., 2021; Danciu et al., 2021; Visini et al., 2021; Woessner et al., 2015), whereas the methodology for the ISS remains that of the previous versions (Basili et al., 2008).
Individual Seismogenic Sources (ISS)
In the ISS construction, the seismic source dimensions (length or width or both) are consistent with the size of the associated earthquake. In the best cases, all dimensions are derived from independent observational data. In the cases of poorer data, either the fault dimensions or the earthquake magnitude can be partly obtained from observational data and the missing information derived from fault scaling relations. Since the ISS layer was designed in the late ’90s, the used scaling relations are those by Wells & Coppersmith (1994). In most cases, the magnitude is obtained from an earthquake catalog or a seismological study and the dimensions are derived from scaling relations (91 cases) and vice versa in the remaining cases (41 cases).
In the ISS construction, the seismic source dimensions (length or width or both) are consistent with the size of the associated earthquake. In the best cases, all dimensions are derived from independent observational data. In the cases of poorer data, either the fault dimensions or the earthquake magnitude can be partly obtained from observational data and the missing information derived from fault scaling relations. Since the ISS layer was designed in the late ’90s, the used scaling relations are those by Wells & Coppersmith (1994). In most cases, the magnitude is obtained from an earthquake catalog or a seismological study and the dimensions are derived from scaling relations (91 cases) and vice versa in the remaining cases (41 cases).
Composite Seismogenic Sources (CSS)
The maximum earthquake magnitude of the CSS is estimated as the magnitude value in the moment magnitude scale, corresponding to the largest possible rupture that the fault can host based on its dimensions.
The relation between the rupture size and the moment magnitude value is derived from the fault scaling relations by Leonard (2010, 2014). Following the definition and geographic distribution of stable continents by Johnston (1994), also adopted by Leonard (2010, 2014), all the faults in version 3.3.0 belong to the interplate category. The variability of all parameters is considered by including the following: 1) the rake which determines whether the dip-slip or the strike-slip relation is used, 2) the width resulting from the combinations of the upper depth, lower depth, and dip angle, 3) the length (end-to-end for coherence with the scaling relations) considering the top and bottom traces, and 4) the standard deviation of the scaling relation. To explore this variability, we randomly sampled the range of all these parameters and developed a distribution of magnitude values from which we retained the 98th percentile.
The maximum earthquake magnitude of the CSS is estimated as the magnitude value in the moment magnitude scale, corresponding to the largest possible rupture that the fault can host based on its dimensions.
The relation between the rupture size and the moment magnitude value is derived from the fault scaling relations by Leonard (2010, 2014). Following the definition and geographic distribution of stable continents by Johnston (1994), also adopted by Leonard (2010, 2014), all the faults in version 3.3.0 belong to the interplate category. The variability of all parameters is considered by including the following: 1) the rake which determines whether the dip-slip or the strike-slip relation is used, 2) the width resulting from the combinations of the upper depth, lower depth, and dip angle, 3) the length (end-to-end for coherence with the scaling relations) considering the top and bottom traces, and 4) the standard deviation of the scaling relation. To explore this variability, we randomly sampled the range of all these parameters and developed a distribution of magnitude values from which we retained the 98th percentile.
Subduction Sources (SDS)
The maximum earthquake magnitude of the SDS is estimated as the magnitude value in the moment magnitude scale, corresponding to the largest possible rupture that the subduction interface can host based on its dimensions, constrained by the upper and lower seismogenic depths.
The relation between the rupture size and the moment magnitude value is derived by the fault scaling relations by Allen & Hayes (2017). The variability of all parameters is considered by including the following: 1) the upper depth, 2) the lower depth, and 3) the standard deviation of the scaling relation. The interface geometry, however, is kept fixed.
The maximum earthquake magnitude of the SDS is estimated as the magnitude value in the moment magnitude scale, corresponding to the largest possible rupture that the subduction interface can host based on its dimensions, constrained by the upper and lower seismogenic depths.
The relation between the rupture size and the moment magnitude value is derived by the fault scaling relations by Allen & Hayes (2017). The variability of all parameters is considered by including the following: 1) the upper depth, 2) the lower depth, and 3) the standard deviation of the scaling relation. The interface geometry, however, is kept fixed.
Discussion
The maximum magnitude estimation for the CSS and SDS depends only on the geometric characteristics of the seismic source; therefore, its potential recurrence or its proneness to releasing earthquakes of such sizes is not considered and should be evaluated separately. In other words, the fact that a CSS or the slab interface of an SDS is associated with a certain maximum magnitude does not inform about the probability or likelihood that that seismic source will ever release an earthquake of that size. One possible use of these estimates is the upper bound of a frequency-magnitude distribution of a given shape and following the moment conservation principle (Anderson & Luco, 1983; Kagan, 2002; Youngs & Coppersmith, 1985).
The maximum magnitude estimation for the CSS and SDS depends only on the geometric characteristics of the seismic source; therefore, its potential recurrence or its proneness to releasing earthquakes of such sizes is not considered and should be evaluated separately. In other words, the fact that a CSS or the slab interface of an SDS is associated with a certain maximum magnitude does not inform about the probability or likelihood that that seismic source will ever release an earthquake of that size. One possible use of these estimates is the upper bound of a frequency-magnitude distribution of a given shape and following the moment conservation principle (Anderson & Luco, 1983; Kagan, 2002; Youngs & Coppersmith, 1985).
References
Allen, T. I., & Hayes, G. P. (2017). Alternative Rupture‐Scaling Relationships for Subduction Interface and Other Offshore Environments. Bulletin of the Seismological Society of America, 107(3), 1240–1253. https://doi.org/10.1785/0120160255
Anderson, J. G., & Luco, J. E. (1983). Consequences of slip rate constraints on earthquake occurrence relations. Bulletin of the Seismological Society of America, 73(2), 471–496. https://doi.org/10.1785/BSSA0730020471
Basili, R., Valensise, G., Vannoli, P., Burrato, P., Fracassi, U., Mariano, S., et al. (2008). The Database of Individual Seismogenic Sources (DISS), version 3: Summarizing 20 years of research on Italy’s earthquake geology. Tectonophysics, 453(1–4), 20–43. https://doi.org/10.1016/j.tecto.2007.04.014
Basili, R., Brizuela, B., Herrero, A., Iqbal, S., Lorito, S., Maesano, F. E., et al. (2021). The Making of the NEAM Tsunami Hazard Model 2018 (NEAMTHM18). Frontiers in Earth Science, 8, 616594. https://doi.org/10.3389/feart.2020.616594
Danciu, L., Nandan, S., Reyes, C., Basili, R., Weatherill, G., Beauval, C., et al. (2021). The 2020 update of the European Seismic Hazard Model: Model Overview. EFEHR Technical Report 001, v1.0.0. Retrieved from https://doi.org/10.12686/a15
DISS Working Group. (2021). Database of Individual Seismogenic Sources (DISS), version 3.3.0: A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas., [Dataset]. https://doi.org/10.13127/DISS3.3.0
Johnston, A. C. (1994). Seismotectonic interpretations and conclusions from the stable continental region seismicity database (The Earthquakes of Stable Continental Regions—v. 1 Assessment of Large Earthquake Potential, A. C. Johnston, K. J. Coppersmith, L. R. Kanter, and C. A. Cornell (Editors) No. Report TR102261V1). Palo Alto, California: Electric Power Research Institute.
Kagan, Y. Y. (2002). Seismic moment distribution revisited: II. Moment conservation principle: Seismic moment distribution revisited: II. Geophysical Journal International, 149(3), 731–754. https://doi.org/10.1046/j.1365-246X.2002.01671.x
Leonard, M. (2010). Earthquake Fault Scaling: Self-Consistent Relating of Rupture Length, Width, Average Displacement, and Moment Release. Bulletin of the Seismological Society of America, 100(5A), 1971–1988. https://doi.org/10.1785/0120090189
Leonard, M. (2014). Self-Consistent Earthquake Fault-Scaling Relations: Update and Extension to Stable Continental Strike-Slip Faults. Bulletin of the Seismological Society of America, 104(6), 2953–2965. https://doi.org/10.1785/0120140087
Visini, F., Pace, B., Meletti, C., Marzocchi, W., Akinci, A., Azzaro, R., et al. (2021). Earthquake Rupture Forecasts for the MPS19 Seismic Hazard Model of Italy. Annals of Geophysics, 64(2), 3. https://doi.org/10.4401/ag-8608
Wells, D. L., & Coppersmith, K. J. (1994). New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the Seismological Society of America, 84(4), 974–1002. https://doi.org/10.1785/BSSA0840040974
Woessner, J., Laurentiu, D., Giardini, D., Crowley, H., Cotton, F., Grünthal, G., et al. (2015). The 2013 European Seismic Hazard Model: key components and results. Bulletin of Earthquake Engineering, 13(12), 3553–3596. https://doi.org/10.1007/s10518-015-9795-1
Youngs, R. R., & Coppersmith, K. J. (1985). Implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates. Bulletin of the Seismological Society of America, 75(4), 939–964. https://doi.org/10.1785/BSSA0750040939
Allen, T. I., & Hayes, G. P. (2017). Alternative Rupture‐Scaling Relationships for Subduction Interface and Other Offshore Environments. Bulletin of the Seismological Society of America, 107(3), 1240–1253. https://doi.org/10.1785/0120160255
Anderson, J. G., & Luco, J. E. (1983). Consequences of slip rate constraints on earthquake occurrence relations. Bulletin of the Seismological Society of America, 73(2), 471–496. https://doi.org/10.1785/BSSA0730020471
Basili, R., Valensise, G., Vannoli, P., Burrato, P., Fracassi, U., Mariano, S., et al. (2008). The Database of Individual Seismogenic Sources (DISS), version 3: Summarizing 20 years of research on Italy’s earthquake geology. Tectonophysics, 453(1–4), 20–43. https://doi.org/10.1016/j.tecto.2007.04.014
Basili, R., Brizuela, B., Herrero, A., Iqbal, S., Lorito, S., Maesano, F. E., et al. (2021). The Making of the NEAM Tsunami Hazard Model 2018 (NEAMTHM18). Frontiers in Earth Science, 8, 616594. https://doi.org/10.3389/feart.2020.616594
Danciu, L., Nandan, S., Reyes, C., Basili, R., Weatherill, G., Beauval, C., et al. (2021). The 2020 update of the European Seismic Hazard Model: Model Overview. EFEHR Technical Report 001, v1.0.0. Retrieved from https://doi.org/10.12686/a15
DISS Working Group. (2021). Database of Individual Seismogenic Sources (DISS), version 3.3.0: A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas., [Dataset]. https://doi.org/10.13127/DISS3.3.0
Johnston, A. C. (1994). Seismotectonic interpretations and conclusions from the stable continental region seismicity database (The Earthquakes of Stable Continental Regions—v. 1 Assessment of Large Earthquake Potential, A. C. Johnston, K. J. Coppersmith, L. R. Kanter, and C. A. Cornell (Editors) No. Report TR102261V1). Palo Alto, California: Electric Power Research Institute.
Kagan, Y. Y. (2002). Seismic moment distribution revisited: II. Moment conservation principle: Seismic moment distribution revisited: II. Geophysical Journal International, 149(3), 731–754. https://doi.org/10.1046/j.1365-246X.2002.01671.x
Leonard, M. (2010). Earthquake Fault Scaling: Self-Consistent Relating of Rupture Length, Width, Average Displacement, and Moment Release. Bulletin of the Seismological Society of America, 100(5A), 1971–1988. https://doi.org/10.1785/0120090189
Leonard, M. (2014). Self-Consistent Earthquake Fault-Scaling Relations: Update and Extension to Stable Continental Strike-Slip Faults. Bulletin of the Seismological Society of America, 104(6), 2953–2965. https://doi.org/10.1785/0120140087
Visini, F., Pace, B., Meletti, C., Marzocchi, W., Akinci, A., Azzaro, R., et al. (2021). Earthquake Rupture Forecasts for the MPS19 Seismic Hazard Model of Italy. Annals of Geophysics, 64(2), 3. https://doi.org/10.4401/ag-8608
Wells, D. L., & Coppersmith, K. J. (1994). New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the Seismological Society of America, 84(4), 974–1002. https://doi.org/10.1785/BSSA0840040974
Woessner, J., Laurentiu, D., Giardini, D., Crowley, H., Cotton, F., Grünthal, G., et al. (2015). The 2013 European Seismic Hazard Model: key components and results. Bulletin of Earthquake Engineering, 13(12), 3553–3596. https://doi.org/10.1007/s10518-015-9795-1
Youngs, R. R., & Coppersmith, K. J. (1985). Implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates. Bulletin of the Seismological Society of America, 75(4), 939–964. https://doi.org/10.1785/BSSA0750040939
