AFTERSHOCK PROBABILISTIC FORECASTING AND TESTING OF OPERABILITY IN EARTHQUAKE FIELD INVESTIGATION ON-SITE:A CASE OF THE 2025 DINGRI MS6.8 EARTHQUAKE IN XIZANG
AFTERSHOCK PROBABILISTIC FORECASTING AND TESTING OF OPERABILITY IN EARTHQUAKE FIELD INVESTIGATION ON-SITE:A CASE OF THE 2025 DINGRI MS6.8 EARTHQUAKE IN XIZANG
On January 7,2025,a MS6.8 earthquake struck Dingri,Xizang,causing significant economic losses and casualties.In response,the China Earthquake Administration launched a multidisciplinary scientific investigation,among which the analysis of sequence characterization and the probability forecasting of large aftershocks is an important and meaningful part of the work.This study aims to enhance the understanding of the aftershock sequence and provide timely scientific support for field investigations.To achieve this,we employ a temporal Epidemic-Type Aftershock Sequence(ETAS)model to perform a real-time tracking analysis of the aftershock sequence over the first seven days following the mainshock.The temporal ETAS model was employed to analyze the evolving characteristics of the aftershock sequence at 0.1-day intervals,and short-term aftershock probability forecasts were generated for the subsequent one-day period.Model performance was evaluated using the Brier Score,a metric that quantifies the agreement between probabilistic forecasts and observed aftershock occurrences.The evaluation focused on different magnitude thresholds to assess the consistency and predictive skill of the model.Key findings from our study include:1)The fitting of ETAS model to observed aftershock activity was generally consistent with reality.The fitted model parameters suggest that the overall decay rate of aftershocks aligns closely with typical sequence decay behaviors(p=1.06).Moreover,the proportion of triggered'offspring'events within the sequence is relatively low(α=1.58),indicating that off-spring events did not heavily dominate the primary aftershock activity.The model's fitting results are consistent with the observed seismic sequence,except for a slight deviation identified around the 220th aftershock,where the observed activity exceeds the expectation based on a homogeneous Poisson process.2)A time-tracking analysis of the model parameters across varying magnitude thresholds reveals that the parameter estimates begin to stabilize approximately 2.8 days after the mainshock.This suggests that incomplete aftershock recordings during the early phase can impact the reliability of early parameter estimation.Thus,early-stage catalog incompleteness should be carefully accounted for in operational forecasting models.3)The model also demonstrates high sensitivity to the occurrence of strong aftershocks.When such events occur,they are quickly reflected in the intensity and frequency curves,demonstrating the model's potential and strong applicability for short-term aftershock forecasting,particularly in a science-based emergency response context.4)Brier score evaluation further supports the model's forecasting effectiveness.For aftershocks above magnitude 3.5,4.0,and 5.0,the forecasting performance consistently exceeds that of a random forecast baseline.Although the model underperforms slightly in forecasting aftershocks above magnitude 4.5 in the early stages,its performance improves over time,especially for magnitude 4.5 and 5.0 events,indicating increasing skill as more data accumulates.These findings highlight the potential of integrating Brier Score evaluation into the temporal ETAS model for assessing probabilistic aftershock forecasts.The results demonstrate that the ETAS model provides valuable operational forecasting capabilities for guiding scientific investigations and emergency response following major earthquakes.The study also identifies key challenges for future improvements,including data completeness,parameter stability,and model adaptability to complex sequences of aftershocks.Moving forward,further refinement of hybrid forecasting approaches-integrating multiple models based on statistical and physics-based methods-could enhance the accuracy and reliability of short-term aftershock forecasting.The operational feasibility of the ETAS model,combined with rigorous evaluation metrics,underscores its role in advancing earthquake forecasting methodologies and supporting earthquake disaster risk reduction in China and beyond.
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