arXiv subjects

Marjan Tourani

Publications and source records attributed to Marjan Tourani.

3 recordsLinked to original sources

arXiv2026

The 2016 Mw 7.0 Kumamoto Earthquake Sequence, Japan revisited: Insights from Spatio-Temporal Analysis of Seismicity Parameters

Understanding how crustal faults accumulate strain, nucleate ruptures, and redistribute post-seismic stress is fundamental to seismic hazard assessment. The 16 April 2016 $M_w$ 7.0 Kumamoto earthquake, rupturing the Futagawa--Hinagu fault zone in the Beppu--Shimabara graben, central Kyushu, Japan, offers a premier dataset for tracking these processes across a full earthquake cycle. Using the JMA catalog (2014--2018) with dynamic completeness estimation ($M_c \approx 2.15$--$2.25$), we examine the Gutenberg--Richter $b$-value, the 3-D hypocentral fractal dimension ($D_c$), and the seismicity-rate anomaly ($Z$-value). During the one- to two-year preparatory phase, $b$ declined from a baseline of $1.35 \pm 0.10$ to a precursory minimum of $0.59$, while $D_c$ contracted from $0.85 \pm 0.15$ to $0.70$--$0.80$, recording stress concentration and microfracture coalescence onto a narrow nucleation zone. A coherent negative $Z$-value anomaly (-1.6 to -2.0) developed along the graben, strengthening with integration time---consistent with, though not proof of, progressive fault locking. Depth-sliced volumes show the low-$b$ locked core ($b \le 0.65$) was stratified at $10$--$12.5$~km depth and sharpened within the final four months before failure. Rupture reversed this within weeks: $b$ surged to $1.25$--$1.35$ and $D_c$ expanded to $2.04$--$2.11$, consistent with coseismic stress drop and aftershock activation, followed by recovery over 2.5 years. Cross-sections reveal sharp aftershock localization alongside two unrelaxed asperities ($b \approx 0.80$--$0.95$) near the Hinagu termination and Mount Aso, consistent with positive Coulomb stress loading. This framework resolves asperity locking, release, and healing better than any single metric; however, since anomalies were identified retrospectively, they should be read as evidence of coherent behavior rather than a validated forecast tool alone.

physics.geo-ph↗

arXiv2026

Cross-Sectional and Spatio-Temporal Analysis of Seismicity Parameters in the Zagros Orogenic Belt: Insights into Crustal Stress Distribution and Seismic Hazard

The Zagros Orogenic Belt, formed by the Arabian-Eurasia collision, is a highly active collision zone hosting a large portion of Iran's seismicity. In this study, the IRSC catalog (2006-2024) was used to construct a homogeneous seismic dataset for the Zagros Belt. We analyzed the spatial and depth distribution of seismicity together with key parameters: b-value, fractal dimension (Dc-value), and differential stress (sigma1 - sigma3) to evaluate stress variations, fault clustering, and seismic hazard. The overall b-value of 0.81 +/- 0.01 indicates an elevated stress state, with persistently low b-value anomalies (0.4-0.7) systematically aligned along major fault zones (Mountain Front Fault, High Zagros Fault, and Main Zagros Reverse Fault). Cross-sectional analyses show that these low b-values (<0.6) are concentrated within the upper ~10 km of the crust, pointing to the shallow brittle layer as the primary zone of stress concentration. The correlation fractal dimension (Dc) ranges from 1.0 to 2.05, with high values (>=1.5) spatially coinciding with low b-value zones, reflecting intense deformation partitioning and structural complexity. This spatial complexity decreases with depth, where lower Dc-values show seismicity localizing onto simpler, discrete planes. Differential stress varies between 100 and 520 MPa (predominantly >=520 MPa) and is strongly anti-correlated with b-value, confirming that low b-values trace critically loaded fault segments. The spatial and depth convergence of these independent parameters confirms that seismic hazard is localized along shallow, highly stressed, and structurally complex fault segments capable of generating future moderate-to-large events. These findings highlight the need for targeted monitoring and hazard mitigation across the region.

physics.geo-ph↗

arXiv2026

Integrating b-Value and Background Seismicity Rate for Spatial Earthquake Forecasting in the Alborz Region, Northern Iran

In this study, we evaluate the spatial forecasting skill of the $b$-value and background seismicity rate $\mu$ 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 $\mu$ 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 $\mu$ zones following long-term seismicity clusters, underscoring their complementary physical roles. Retrospective testing confirms this complementarity: the combined $b$--$\mu$ 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.

physics.geo-ph↗