Crustal thickness and average V p /V s ratio variations in northern Vietnam from teleseismic receiver functions Van-Duong Nguyen Bor-Shouh Huang Tu-Son Le Van-Toan Dinh Lupei Zhu CTBTO-S&T2011
Outline 1. Introduction 2. Teleseismic receiver functions analysis 3. H-κ stacking algorithm 4. Broadband seismic dataset 5. Results and Discussion 6. Conclusion
Study area After Tapponier et. al (1982), revised by T. Mark Harison et. al (1986)
Sketch map of tectonic and seismicity in northern Vietnam
The objective of this research: Applying the receiver function analysis to study Moho depth variation and the Vp/Vs ratio in northern Vietnam. To study the relation between the characteristics of crustal structure and the tectonic elements in the region.
Teleseismic receiver functions analysis H David Wilson et al., 2003
H-κ stacking algorithm
Broadband seismic dataset More than 200 events M >= 5.5 90 0 60 0 30 0 < D <90 0 30 0
Results and Discussion Receiver functions at HGVB
The (H-κ) estimated result for HGVB station
CHINA Legend: Neotectonics zoning map LAOS LCVB DBVB Ma R. F. TGVB Dien Bi en - L ai Chau F. SPVB SLVB Chay R. F. Red River Shear Zone TTVB MCVB HGVB VTVB Ma R. F. DHVB HBVB LAVB Lo R. F. CBVB BCVB MTVB BGVB LSVB Thuong R. F. HN1B PLVB DSVB Tonkin Bay THVB TIYB TECTONIC BLOCKS South China Orogenic Zone Viet Bac tectonic block An Chau - Duyen Hai tectonic block Red River Shear Zone Indochina Orogenic Zone Northwest tectonic block Truong Son tectonic block CCVB k m2 0 10 0 20 40 60 80km Muong Te tectonic block New collapse-created tectonic block VIVB
The Moho depth at each station 24 102 104 106 108 Moho depth ranging from 26.5 to 36.4 km and the average depth is 30.9 km 22 20 HGVB CBVB SPVB VTVB LCVB BCVB LSVB TGVB DHVB DBVB TTVB MTVB SLVB BGVB HN1B NW MCVB HBVB PLVB DSVB LAVB NE THVB RRD TIYB CCVB VIVB 18 20 km 30 km 40 km
The V p /V s ratio (κ) 24 102 104 106 108 The V p /V s ratio ranging from 1.64 to 1.82 and the average ratio is 1.71 22 HGVB CBVB NE SPVB VTVB LCVB BCVB LSVB TGVB DHVB DBVB TTVB MTVB SLVB BGVB HN1B NW MCVB HBVB PLVB DSVB TIYB 20 LAVB THVB RRD CCVB VIVB 18 1.62 1.72 1.82
1.4 1.5 1.6 1.7 1.8 1.9 2 10 15 20 25 30 35 40 45 50 MTVB LSVB BCVB CBVB DHVB VTVB HGVB HBVB MCVB SLVB TTVB TGVB DBVB LCVB SPVB VIVB CCVB THVB LAVB DSVB HN1B PLVB BGVB TIYB (b) (a) MTVB LSVB BCVB CBVB DHVB VTVB HGVB HBVB MCVB SLVB TTVB TGVB DBVB LCVB SPVB VIVB CCVB THVB LAVB DSVB HN1B PLVB BGVB TIYB NE NW RRD NE NW RRD
Comparison with previous studies Geological structure from seismic profile interpretation BCVB HBVB Moho
Moho depth vs. Bouguer gravity anomaly for northern Vietnam 38 36 34 32 y = -0.0412x + 28.3 R 2 = 0.6327 km 30 28 26 24-180 -160-140 -120-100 -80-60 -40-20 0 20 mgl Moho depths vs. Bougher anomaly Linear (Moho depths vs. Bougher anomaly)
Estimated Moho depths from other studies 45 40 35 Moho depth (km) 30 25 20 NW 15 MTVB LSVB BCVB CBVB DHVB VTVB HGVB HBVB MCVB SLVB TTVB TGVB DBVB LCVB SPVB VIVB CCVB THVB LAVB DSVB HN1B PLVB BGVB TIYB Hai D. T., 2003; Toan et al., 2010; This study;
Conclusion The Moho depths vary from 26.5km (THVB) to 36.4km (SPVB). The Moho depth deepens gradually landward from southeast to northwest. The Moho depths in Northwest are higher than the others. Moho depths are well correlated with Bougher anomaly. The V p /V s ratio varies from 1.64 to 1.82 (lower than global ratio 1.78) and probably depends on the physical properties of rocks in each region. NW section high ratios partial melting, upwelling, and more mafic/ultramafic composition. NE and RRD sections low ratios more felsic composition and belonging to the craton of South China block