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We propose an interdisciplinary approach to time-dependent neo-deterministic seismic hazard assessment (T-NDSHA) for the China Seismic Experimental Site (CSES) at a 1-year time scale. The approach is based on the neo-deterministic seismic hazard assessment (NDSHA), with the “controlling” earthquakes (or “scenario” earthquakes) as defined by the Annual Consultation on the Likelihood of Earthquakes. The Annual Consultation, organized by the China Earthquake Administration (CEA), has been an interdisciplinary practice since 1972, with the output of “alert regions” with increased probabilities of strong earthquakes, featured by real forward forecasting characteristics. We take the year 2014, in which there were four strong earthquakes in the CSES region, as a showcase example to illustrate how the T-NDSHA may be conducted and evaluated. Considering the alert regions provided by the Annual Consultation, the expected strong ground motion parameters and the macroseismic intensities are mapped by the NDSHA algorithms considering the regional Earth structures and the focal mechanisms of historical earthquakes. The estimated intensities are then subjected to comparison with the intensities produced by the actual earthquakes. Evaluation of the performance of such annual seismic hazard assessment is performed using a confusion matrix and Molchan error diagram, respectively, indicating that the combination of the NDSHA and the annual forecasting provides the emergency preparation with a ready-to-use mapping of expected intensities which outperforms random forecasting. The proposed approach provides a substantial improvement to the Annual Consultation, and it can naturally be applied to other regions where intermediate-term middle-range earthquake forecasts are available and where the need for emergency preparation are duly considered.

In recent years, probabilistic seismic hazard assessment (PSHA) has been the most common procedure to evaluate the potential effects of future earthquakes. It assesses the probability that some measure of ground motion intensity (e.g., the peak ground acceleration) exceeds some threshold during a given period of time (most commonly 10% in 50 years’time). In Europe and the Mediterranean region, different efforts starting in the 1990s have provided several regional hazard models at the continental scale (e.g., Jiménez et al., 1999, 2001; Giardini et al., 2003) with the latest model in Woessner et al. (2015) deriving a complete set of harmonized seismic hazard results and associated uncertainties for Europe. Site studies for nuclear power plants were the onset for the development of seismic hazard in Spain at the beginning of the 1970s. At that time, the existing regulations demanded classical deterministic analysis. Therefore, only a few works included either statistical or probabilistic approaches, which later on were widely applied in most of the regional hazard studies carried out in Spain in the 1980s and 1990s (see, e.g., Martín, 1984; Muñoz et al., 1984; Litehiser and Marrone, 1991, among others). It was for the first time in 1994 when the update of the Spanish Building Code incorporated a probabilistic seismic hazard map to define the basic seismic action (Martín, 1995). Studies incorporating alternative statistical analysis, including Bayesian techniques, of hazard parameters were also applied in the last 1980s and early 1990s (see, e.g., García-Fernández et al., 1989; Egozcue et al., 1991)

Carbon dragged at sub-arc depths and sequestered in the asthenospheric upper mantle during cold subduction is potentially released after millions of years during the breakup of continental plates. However, it is unclear whether these deep-carbon reservoirs can be locally remobilized on shorter-term timescales. Here we reveal the fate of carbon released during cold subduction by analyzing an anomalously deep earthquake in December 2020 in the lithospheric mantle beneath Milan (Italy), above a deep-carbon reservoir previously imaged in the mantle wedge by geophysical methods. We show that the earthquake source moment tensor includes a major explosive component that we ascribe to carbon-rich melt/fluid migration along upper-mantle shear zones and rapid release of about 17,000 tons of carbon dioxide when ascending melts exit the carbonate stability field. Our results underline the importance of carbon-rich melts at active continental margins for emission budgets and suggest their potential episodic contributions to atmospheric carbon dioxide.