Abstract
Abstract Over the last 500 years, an average of five intermediate-depth earthquakes of Mw = 7 and larger have occurred during each 100-year period in Vrancea, Central Romania. We have therefore attempted to assess the long-term seismic hazards in Vrancea using a stress-release (SR) model which models the elastic rebound theory in a stochastic process. The hypocenter catalog, ROMPLUS, provided by the National Institute for Earth Physics (NIEP), was adopted for the study. We only used data on earthquakes located in Vrancea and applied the SR-model to data sets of earthquakes with a magnitude of 7.0 and larger for three different time periods. Renewal models, such as the Brownian and Weibull model, were also applied to the same data set, but these did not perform as well as the SR-model. The SR-model can assess future earthquake probability and has identified that the probability of an earthquake occurring in Vrancea in a 5-year period exceeds 40% by the end of this decade.
Highlights
Large, intermediate-depth earthquakes occur frequently in Vrancea, Central Romania
The seismic activity in Vrancea is characterized by location-specific features: (1) strong earthquakes occur at intermediate depths in a very small volume; (2) Vrancea is located at the SE corner of the Carpathian arc; (3) there is no evidence of an active subduction system
Because renewal-process models are used for hazard assessment in both the United States (Working Group on California Earthquake Probabilities, 1999) and Japan (Shimazaki et al, 1999), we compared actual data from renewal models with the results from the SR-model
Summary
Intermediate-depth earthquakes occur frequently in Vrancea, Central Romania. Over the past 500 years, an average of five earthquakes of M = 7.0 and greater have occurred each 100-year period. Renewal-process models, such as the Brownian, lognormal, Weibull, and Gamma models, are normally used for assessing the long-term probability of characteristic earthquake sequences of quasi-periodic recurrence (Working Group on California Earthquake Probabilities, 1990, 1999; Shimazaki et al, 1999). We have applied the stress-release model (SRmodel; see Zheng and Vere-Jones, 1991) to assess the seismic hazard in Vrancea This model formulates the gradual build-up of stress by tectonic movements and release of that stress in the form of earthquakes. Imoto (2001) applied the SR-model to the Nankai earthquake sequence, in southwestern Japan, comparing the model with renewal models and concluding that the SR-model was better than the renewal model in terms of information quantity These investigations imply that the SR-model is applicable to both characteristic earthquake sequences and events governed by a simple stress regime.
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