Abstract
<title>Abstract</title> <p>The eastern Alborz is one of the most tectonically active regions of northern Iran, yet its crustal structure remains poorly constrained. Local earthquake tomography was performed using P- and S-wave travel-time data recorded by temporary and permanent seismic networks between 2007 and 2008. Following quality control, 2,048 local earthquakes recorded by 32 seismic stations were selected for the simultaneous inversion of earthquake hypocenters and seismic velocities with the LOTOS algorithm. Resolution tests indicate that the final models reliably recover the major velocity anomalies within the well-sampled parts of the crust. The resulting Vp, Vs, and Vp/Vs models reveal pronounced lateral heterogeneity and crustal segmentation. Extensive low-velocity anomalies spatially coincide with the principal active fault systems and relocated seismicity, indicating that active deformation is preferentially localized within mechanically heterogeneous crustal domains. The models also reveal two previously unrecognized low-velocity lineaments in the southeastern part of the study area, suggesting the presence of concealed fault-related structures. A persistent low-velocity anomaly associated with relatively elevated Vp/Vs values is also observed beneath the Damavand volcanic center. These results provide a seismic velocity model of the eastern Alborz and offer new constraints on crustal segmentation, concealed fault-related structures, and the relationship between seismic velocity heterogeneity and active deformation. They also provide an improved geophysical framework for understanding active tectonics and assessing seismic hazard within the northern sector of the Arabia–Eurasia collision zone.</p>