Integrating b-Value and Background Seismicity Rate for Spatial Earthquake Forecasting in the Alborz Region, Northern Iran
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arXiv
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| Natura: | Preprint |
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2026
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| author | Mousavi, Muhammed Hossein Mohammadigheymasi, Hamzeh Alavijeh, Parva Sadeghi Tourani, Marjan |
| author_facet | Mousavi, Muhammed Hossein Mohammadigheymasi, Hamzeh Alavijeh, Parva Sadeghi Tourani, Marjan |
| contents | In this study, we evaluate the spatial forecasting skill of the $b$-value and background seismicity rate $μ$ across the Alborz region using a homogenized catalog of 23,961 earthquakes ($M \geq 1.5$) recorded by the Iranian Seismological Center between 2006 and 2024. Forecast performance for $M \geq 4.0$ and $M \geq 4.5$ is assessed using Molchan error diagrams, probability gain, probability difference, and the modified area skill score. The results show that $μ$ provides a consistently strong spatial signal, with Molchan curves well below the random baseline and probability gains of 5--6 at low alarm rates, reflecting the persistent clustering of seismicity along major Alborz faults. The $b$-value exhibits limited skill at lower magnitudes but improves steadily with increasing magnitude; its skill score becomes positive above $M \approx 5.3$, indicating that $b$-value anomalies begin to capture meaningful stress concentrations only for larger events. Spatial patterns reveal low $b$ zones along active reverse and strike-slip structures and high $μ$ zones following long-term seismicity clusters, underscoring their complementary physical roles. Retrospective testing confirms this complementarity: the combined $b$--$μ$ forecast achieves detection rates of 0.81--0.83 at spatial alarm rates of 0.43 and 0.36 for $M \geq 4.0$ and $M \geq 4.5$, respectively, representing the most efficient forecast configuration among all tested models. These findings demonstrate that integrating stress-state and tectonic-loading indicators yields a more efficient and physically grounded framework for operational earthquake forecasting in the Alborz region. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_23494 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Integrating b-Value and Background Seismicity Rate for Spatial Earthquake Forecasting in the Alborz Region, Northern Iran Mousavi, Muhammed Hossein Mohammadigheymasi, Hamzeh Alavijeh, Parva Sadeghi Tourani, Marjan Geophysics In this study, we evaluate the spatial forecasting skill of the $b$-value and background seismicity rate $μ$ across the Alborz region using a homogenized catalog of 23,961 earthquakes ($M \geq 1.5$) recorded by the Iranian Seismological Center between 2006 and 2024. Forecast performance for $M \geq 4.0$ and $M \geq 4.5$ is assessed using Molchan error diagrams, probability gain, probability difference, and the modified area skill score. The results show that $μ$ provides a consistently strong spatial signal, with Molchan curves well below the random baseline and probability gains of 5--6 at low alarm rates, reflecting the persistent clustering of seismicity along major Alborz faults. The $b$-value exhibits limited skill at lower magnitudes but improves steadily with increasing magnitude; its skill score becomes positive above $M \approx 5.3$, indicating that $b$-value anomalies begin to capture meaningful stress concentrations only for larger events. Spatial patterns reveal low $b$ zones along active reverse and strike-slip structures and high $μ$ zones following long-term seismicity clusters, underscoring their complementary physical roles. Retrospective testing confirms this complementarity: the combined $b$--$μ$ forecast achieves detection rates of 0.81--0.83 at spatial alarm rates of 0.43 and 0.36 for $M \geq 4.0$ and $M \geq 4.5$, respectively, representing the most efficient forecast configuration among all tested models. These findings demonstrate that integrating stress-state and tectonic-loading indicators yields a more efficient and physically grounded framework for operational earthquake forecasting in the Alborz region. |
| title | Integrating b-Value and Background Seismicity Rate for Spatial Earthquake Forecasting in the Alborz Region, Northern Iran |
| topic | Geophysics |
| url | https://arxiv.org/abs/2605.23494 |