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The Linfen rift is a Cenozoic extensional rift with significant seismicity and seismic hazards. Studies of this rift shed light on deep dynamic processes and seismogenic mechanisms relevant to crustal structure and seismic activity. We first conducted a joint inversion of receiver functions and surface wave dispersion on waveform data collected from 27 broadband seismic stations to image the crustal S-wave velocity in the Linfen rift and its surroundings. We then relocated the source parameters for 10 earthquake events with depths>20 km and studied the relationship between crustal S-wave velocity and seismicity. The results show that low-velocity zones of different scales exist in the middle-lower crust, and that the depth of the seismogenic layer gradually increases from ~25 km in the south to ~34 km in the north, roughly corresponding to the bottom of the low-velocity zone.We found that most of the relocated earthquakes occurred in the low-velocity zone at depths of 18 km to 34 km, with the deepest at 32 km. Two of the greatest historic earthquakes, Linfen (Ms 7.75) in 1695 and Hongtong (Ms 8.0) in 1303, occurred at the bottom of the high-velocity zone at depths of 12 km to 18 km. Our results, combined with previous studies, suggest that the upwelling mantle material below the rift did not remarkably affect the velocity structure from the bottom of the seismogenic layer down to the uppermost mantle nor heat the crust. It is likely that neither crustal-scale faults nor mantle earthquakes exist in the Linfen rift. [ABSTRACT FROM AUTHOR]

Using teleseismic waveform records from 363 broadband stations, we applied H-κ stacking of receiver functions to estimate crustal thickness ( H) and average Vp/Vs ratio ( κ) in the central and western North China Craton (NCC) and adjacent regions. Our results show that, except for thinning in the Cenozoic rifts and southern edge of the central NCC, H gradually thickens westward from ~30 km at the easternmost edge of the central NCC to >60 km near the northeastern margin of the Tibetan Plateau. κ exhibits complex variations, with locally high or low anomalies in the rifts, at the southern edge of the central NCC and at tectonic boundary zones. Low-density uppermost mantle and distinct N-S differences are observed in the Ordos, suggesting typical cratonic crust. Thickened crust and complex variations in κ at the southwestern boundary of the Ordos may be related to the formation of the Palaeozoic Qilian Block and late uplift of the Tibetan Plateau. Thinned crust and locally high κ are observed in and near the Cenozoic rifts, suggesting complex crustal modifications that may have been caused by repeated reactivation at pre-existing weak zones by successive thermal-tectonic events. Thin crust and low κ are found at the southern edge of the central NCC, suggesting crustal modifications such as delamination, especially in the lower crust, which may be related to collision of the NCC and Yangtze Block. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY We obtained the crustal thickness ( H) and average Vp/ Vs ratio (κ) for the central (CNCC) and western North China Craton (WNCC) by H-κ stacking of receiver functions. Our results show that H and κ varies significantly but similarly in the northern and southern CNCC, reflecting possible effects of the Phanerozoic cratonotic reactivation on the region. Of the WNCC, the south is featured by κ values typical for Precambrian shields (∼1.77) and variations of H mirroring surface topography; the north presents large fluctuations of κ (1.68-1.93) and a crustal thickening (up to 50 km) uncorrelated with topography. Such N-S differences were thought to be associated with a ∼1.95-Ga suturing event occurred in the north with little effects on the south. Our observations suggest that distinct structural heterogeneities of the NCC not only reflect diverse regional tectonics in Phanerozoic, but also provide evidence for long-term survival of crustal fabrics in stable continental interior. [ABSTRACT FROM AUTHOR]