Crustal structure in the Changbaishan volcanic area, China, determined by modeling receiver functions

Three‐dimensional density modeling of the EGM2008 gravity field over the Mount Paekdu volcanic area

“…In contrast, the most recent seismic study [Song et al, 2007] concluded that midcrustal LVZs do not exist directly under Mount Paekdu but that one LVZ exists in the crust under the place about 70 km north of the caldera lake ( Figure 3b). A receiver function analysis [Hetland et al, 2004] resolved LVZs both beneath Mount Paekdu and in the area to the north. We evaluate these different findings using gravity modeling in section 6.…”

“…The gravity anomalies computed from the model (green line in Figure 14a) are not consistent with the observed anomalies (black line in Figure 14a), producing a remarkable difference of >30 × 1À0 5 m/s 2 over the LVZ, 100 to 150 km along the profile. The second model characterized two LVZs, one located under Mount Paekdu and one under the region to the north of Mount Paekdu (Figure 14c) [Hetland et al, 2004]; this result also yields a large inconsistency between computed anomalies (blue line in Figure 14a) and observed anomalies. The results of these different density models indicate that the location of the LVZ is confined to Mount Paekdu (Figure 14b), and the other possible location to the north is incompatible within the constraints of the data and modeling.…”

“…The most recent seismic interpretation [Song et al, 2007] suggested that a midcrustal LVZ might exist under the region 70 km to the north of Mount Paekdu, while most other previous results [e.g., Tang et al, 1998;Zhang et al, 2002aZhang et al, , 2002b indicated that the LVZ should lie only under Mount Paekdu. The receiver function study of Hetland et al [2004] resolved LVZs under both areas. In section 6, we modeled density structures along the A-P-A′-A″ seismic profile as proposed by the previous seismic interpretation of Zhang et al [2002aZhang et al [ , 2002b and explained that the low Bouguer anomalies found over Mount Paekdu are caused by the combined gravity effects of the deep Moho, LVZs with lower densities than the surrounding material, volcanic rocks covered by other deposits in the area, and the predicted magma chamber underneath the volcano.…”

“…The gravity effect of the Moho was calculated from an isostatic gravity field and topography by using an Airy-Heiskanen model with a density contrast of 350 kg/m 3 between the lower crust and the upper mantle. The deepest [Tang et al, 1998;Shin and Baag, 2000;Zhang et al, 2002aZhang et al, , 2002bHetland et al, 2004;Song et al, 2007]. The gravity effect due to the variation in depth of the Moho is then calculated by applying the Parker-Oldenburg algorithm [Parker, 1972;Oldenburg, 1974] assuming a crust-mantle density contrast of 350 kg/m 3 .…”

“…Furthermore, the most negative local anomaly of about À40 × 10 À5 m/s 2 coincides with the location of the Cheonji caldera lake, under which a deep-reaching magma chamber evidently exists [Tang et al, 1998;Zhang et al, 2002aZhang et al, , 2002bHetland et al, 2004]. Positive anomalies of >60 × 10 À5 m/s 2 mapped along the coast can be explained by mantle material uplifted into the lower crust [Pak et al, 1993].…”