EPP

The Tan-Lu fault zone is a large NNE-trending fault zone in eastern China. Investigations of the structures of the fault zone and its surrounding areas have attracted much attention. In this study, we used dense-array ambient noise tomography to construct a three-dimensional shear wave velocity model of shallow crust in an area about 80km × 70km in Lujiang, Anhui Province, eastern China. For approximately one month we collected continuous ambient noise signals recorded by 90 short-period seismographs in the region, and obtained the short-period Rayleigh wave empirical Green's functions between stations by the cross-correlation method; we also extracted 0.5–8 s fundamental mode Rayleigh wave group velocity and phase velocity dispersion curves. Based on the direct surface wave tomography method, we jointly inverted the group velocity and phase velocity dispersion data of all paths and obtained the 3-D shear wave velocity structure in the depth range of 0–5 km. The results revealed important geological structural features of the study area. In the north region, the sedimentary center of the Hefei Basin — the southwestern part of the Chaohu Lake — shows a significant low-velocity anomaly to a depth of at least 5 km. The southwestern and southeastern regions of the array are the eastern margin of the Dabie orogenic belt and the intrusion area of Luzong volcanic rocks, respectively, and both show obvious high-speed anomalies; the sedimentary area within the Tan-Lu fault zone (about 10 km wide) shows low-velocity anomalies. However, the volcanic rock intrusion area in the fault zone is shown as high velocity. Our shallow crustal imaging results reflect the characteristics of different structures in the study area, especially the high-speed intrusive rocks in the Tan-Lu fault zone, which were probably partially derived from the magmatic activity of Luzong volcanic basin. From the Late Cretaceous to Early Tertiary, the Tan-Lu fault zone was in a period of extensional activity; the special stress environment and the fractured fault zone morphology provided conditions for magma in the Luzong volcanic basin to intrude into the Tan-Lu fault zone in the west. Our 3-D model can also provide important information for deep resource exploration and earthquake strong ground motion simulation.

Previous studies have reported that, before or after occurrences of strong earthquakes, some low earth orbit satellites recorded ionospheric disturbances, including electromagnetic emissions and plasma fluctuations over the epicenter region or its conjugate point. Theoretically speaking, due to some electromagnetic coupling effect, electromagnetic emissions from the earthquake preparation zone could propagate from the lithosphere to the atmosphere, and could reach the ionosphere, even up to the inner magnetosphere. This paper introduces the electric field detector (EFD) onboard the ZhangHeng-1 satellite (ZH-1). The EFD is designed to measure electric field fluctuations within the broad frequency range of DC to 3.5 MHz, divided into 4 channels: ULF (DC–16 Hz), ELF (6 Hz–2.2 kHz), VLF (1.8 kHz–20 kHz) and HF (18 kHz–3.5 MHz). The sampling rates of the channels are 125 Hz, 5 kHz, 50 kHz and 10 MHz, respectively. The EFD includes 4 spherical probes mounted on a over 4.5 m boom and an electronic box inside the satellite module. The resolution of the EFD is 1 μV·m^-1·Hz^-1/2 at frequencies from DC to 16 Hz, and the sensitivity is 0.1 μV·m^-1·Hz^-1/2 at frequencies from 6 Hz to 2.2 kHz, 0.05 μV·m^-1·Hz^-1/2 in the band 1.8 kHz to 20 kHz, and 0.1μV·m^-1·Hz^-1/2 from 20 kHz to 3.5 MHz. The dynamic range from DC to 20 kHz is over 120 dB, and over 96 dB from 20 kHz to 3.5 MHz. The EFD has two observation modes: survey mode and burst mode. The survey mode concentrates primarily on electric field power density values; the burst mode provides high sampling rate waveform data. The detailed configuration of the EFD onboard the ZH-1 is also introduced in this paper. During the six months’ orbit test phase, the EFD recorded a number of natural electromagnetic emissions. Preliminary analysis of these data suggests that the EFD performs well onboard the ZH-1 and is meeting the requirements of the scientific objectives of ZH-1.