Abstract: Using 1861 P wave arrival times from 460 local earthquakes (M_L≥1.0) recorded by the Handan Seismic Network from 2001 to 2008, we use the simultaneous inversion method to determine the hypocentral distribution and velocity structure in the juncture area (35.0°～38.0°N,113.0°～116.0°E) of Shanxi, Hebei, Shandong and Henan provinces. T④he results show that: ① After the simultaneous inversion of earthquake relocation and velocity structure, residual root mean square (RMS) of P wave travel time decreased from the 1.35 s to the 0.45 s, location error averaged 0.031 km in the EW direction, 0.029 km in the NS direction, and average 0.060 km vertically. ② Small and medium earthquakes spread in the NEE direction in the Xingtai hypocentral area, with focal depths varying from 7 to 14 km; seismicity displays two conjugated distributions in the directions of NEE and NNW in the Cixian hypocentral area with focal depths varying from 8 to 18 km. The focal depths become shallower form south to north in the juncture area. ③ Low velocity layer exists in 7~14 km beneath the meizoseismal area of Xingtai earthquake, consistent with the focal depth of Xingtai M7.2 earthquake; low velocity layer also exists in 13~18 km beneath the meizoseismal area of Cixian earthquake, consistent with the focal depth of Cixian M7.5 earthquake. The velocity structure of Cixian hypocentral area is much complicated than that of Xingtai hypocentral area.

Key words: Simultaneous inversion, Earthquake location, Velocity structure, Juncture of Shanxi, Hebei, Shandong and Henan