Source Process-Related Delays in Earthquake Early Warning for Example Cases in Greece

ABSTRACT We explore a hypothetical zero-latency earthquake early warning (EEW) system in Greece, aiming to provide alerts before warning thresholds of the intensity of ground motion are exceeded. Within the seismotectonic context of Greece, both shallow- and intermediate-depth earthquakes (along the Hellenic subduction zone) are plausible and, thus, examined. Using regionally applicable attenuation relations, we combine and adjust the methodologies of Minson et al. (2018) and Hoshiba (2020) to examine what are the minimum magnitudes required to invoke the warning thresholds at the user site. With simple modeling, we examine how fast an alert can be issued and what is the available warning time when taking into account delays due to finite-fault rupture propagation, alongside other delays. These computations are merged with delays introduced due to the present-day configuration of the Greek national monitoring network (varying spatial density of permanent monitoring stations). This approach serves as a tool to assess the feasibility of an EEW system at specific sites and to redesign the national permanent monitoring network to serve such a system more effectively (we provide results for four sites.). Warning times for on-land crustal earthquakes are found to be shorter, whereas for intermediate-depth earthquakes in Greece an EEW system is feasible (provides warning times of several tens of seconds at large cities, e.g., on Crete Island) even with the current configuration of the national monitoring network, which is quite sparse in the southern part of the country. The current network configuration also provides sufficient early warning (e.g., of the order of 10 s for a warning threshold of 0.05g) at the center of Athens from earthquakes of the eastern Gulf of Corinth—a zone posing elevated hazard in the broader area of the Greek capital. Several additional assumptions and factors affecting the operability of an EEW system in Greece (i.e., source process complexity and uncertainty in attenuation laws) are also discussed.

Analysis of Differences in Seismic Moment Tensors between Global Catalogs

<p>Catalogs of moment tensors form the foundation for a wide variety of studies in seismology. Despite their importance, assessing the uncertainties in the moment tensors and the quantities derived from them is difficult. To gain insight,<span>  </span>we compare 5000 moment tensors in catalogs of the USGS and the Global CMT Project for the period from September 2015 to December 2020. The GCMT Project generally reports larger scalar moments than the USGS, with the difference between the reported moments decreasing with magnitude. The effect of the different definitions of the scalar moment between catalogs, reflecting treatment of the non-double-couple component, is consistent with that expected. However, this effect is small and has a sign opposite to the differences in reported scalar moment. Hence the differences are intrinsic to the moment tensors in the two catalogs. The differences in the deviation from a double-couple source and in source geometry derived from the moment tensors also decrease with magnitude. The deviations from a double-couple source inferred from the two catalogs are moderately correlated, with the correlation stronger for larger deviations. However, we do not observe the expected correlation between the deviation from a double-couple source and the resulting differences in scalar moment due to the different definitions. There is essentially no correlation between the differences in source geometry, scalar moment, or fraction of the non-double-couple component, suggesting that the differences reflect aspects of the inversion rather than the source process. Despite the differences in moment tensors, the reported location and depth of the centroids are consistent between catalogs.</p>

Source Process of the 24 January 2020 Mw 6.7 East Anatolian Fault Zone, Turkey, Earthquake

The 24 January 2020 Mw 6.7 earthquake in eastern Turkey was due to the reactivation of the strike-slip faulting between the Arabian and Anatolian plates. To gain insight into the source regime and its relationship with historical earthquakes, we determined the coseismic slip distribution of this event by joint analyses of Interferometric Synthetic Aperture Radar and teleseismic observations. Inversion results indicate that the main rupture asperity occurred in the southwest of the epicenter with a maximum slip of ∼1.9 m, showing a bilateral source process with an average rupture velocity of ∼1.6 km/s, and small slip extended to the surface near the epicenter. The estimated seismic moment is 1.4×1019 N·m, associated with a ∼50 km long and ∼15 km wide fault plane. The aftershocks distribution is obviously complementary with the coseismic rupture zone. That is, the majority of aftershocks clustered in the transitional regions from the large to small slip areas. The 2020 earthquake only ruptured part of the locked zone and could increase the seismic activity in the East Anatolian fault zone during the interseismic phase. Two verified seismic gaps remain unbroken and hazardous.