Analysis of In-situ Stress Measurement and Real-time Monitoring Results in Nyching of Tibetan Plateau and Its Response to Nepal MS8.1 Earthquake

Abstract

Abstract:

To explore the in-situ stress in the fracture belt and its present activity, the authors gathered data from hydraulic fracturing for in-situ stress measurement and from piezomagnetic method for monitoring relative magnitude of in-situ stress along the drilling hole with total depth of 300 meters located in a granite-rich region in the northern part of Nyching, Tibet. The measurements of in-situ stress indicate the relationship of SH>Sh≥SV, and the structure features of shallow earth’s crust rock formation reveal that current horizontal principal stresses play a leading role in reverse fault activity. Moreover, the measured maximum principal in-situ stress strikes in NNE direction, reflecting present compressive properties with dextral slip activity of faulting to north-east and near-south-north trend. Calculated through measured principal stresses, the magnitudes of feature parameters (μm) are obtained to be in the range of 0.11 to 0.23, which reflect a lower-stress accumulative capability of the regional crust and inactivity of fault movement in this area. Although the direction of the maximum horizontal principal stress remains basically unchanged in the occurrence of Nepal M_S8.1 earthquake, the stress-monitoring results show that before the earthquake the values of the maximum and minimum horizontal principal stresses increase in 0.35 MPa and 0.24 MPa, respectively; during the earthquake for the co-seismic effect the reduced values are 0.05 MPa and 0.04 MPa, respectively; while four months later after the earthquake the maximum horizontal principal stress is reduced by 0.05 MPa, and the minimum principal stress increases by 0.01 MPa. Based on the in-situ stress measuring and real-time monitoring results while the earthquakes happen, the change of stress fields can be investigated to understand the activity of regional faults and it is much significant for the study of seismic risk and crustal stability.

Key words: in-situ stress measurement, in-situ stress monitoring, seismic hazard, Nepal M_S8.1 earthquake

CLC Number:

P642.2

ZHANG Peng, QU Yaming, GUO Changbao, FENG Chengjun, MENG Wen, FAN Yulu, TAN Chengxuan, WANG Lei. Analysis of In-situ Stress Measurement and Real-time Monitoring Results in Nyching of Tibetan Plateau and Its Response to Nepal M_S8.1 Earthquake[J]. Geoscience, 2017, 31(05): 900-910.

Figures/Tables 13

Fig.1 Distribution map of main active faults and seismic centers in the research area

Table 1 Results of hydraulic fracturing in-situ stress measurements of Bayi drilling hole in Nyching Tibet

序号	压裂段中心深度/m	P_H/MPa	P_o/MPa	P_b/MPa	P_r/MPa	P_s/MPa	S_h/MPa	S_H/MPa	S_v/MPa	T/MPa	S_H方向
1	56.60	0.57	0.31	14.00	4.25	3.70	3.70	6.54	1.50	9.75
2	71.40	0.71	0.45	12.39	6.11	5.59	5.59	10.21	1.89	6.28
3	76.36	0.76	0.50	18.21	9.39	6.66	6.66	10.09	2.02	8.82
4	102.50	1.03	0.77	10.83	3.71	2.74	2.74	3.74	2.72	7.12
5	115.00	1.15	0.89	13.58	4.97	4.18	4.18	6.68	3.05	8.61
6	125.50	1.26	1.00	12.21	4.93	4.26	4.26	6.85	3.33	7.28
7	137.50	1.38	1.12	10.59	3.81	3.22	3.22	4.73	3.64	6.78
8	149.20	1.49	1.23	10.77	4.63	3.66	3.66	5.12	3.95	6.14
9	182.30	1.82	1.56	13.63	7.01	5.63	5.63	8.32	4.83	6.62	NE31°
10	188.40	1.88	1.62	17.35	8.68	6.28	6.28	8.54	4.99	8.67
11	208.00	2.08	1.82	17.84	9.41	6.44	6.44	8.09	5.51	8.43	NE21°
12	250.20	2.50	2.24	16.69	8.78	7.88	7.88	12.62	6.63	7.91

Fig.2 Calibration curves of component magnetic stress sensors of Bayi drilling hole in Nyching

Fig.3 Installation orientation of component magnetic stress sensors in Bayi drilling hole in Nyching

Fig.4 Results of stress monitoring in Nyching in the 2015 Nepal earthquake event(20150124-20150825)

Fig.5 Diagram showing three directions(angle of 45°) of the normal(or change) stress(or change) and main stress

Table 2 Results of initial horizontal principal stress and stress tensors

$σ H m a x 0$ /MPa	$σ h m i n 0$ /MPa	$σ v 0$ /MPa	$σ x x 0$ /MPa	$σ y y 0$ /MPa	$τ x y 0$ /MPa	σ_Hmax方向
6.92	4.70	2.51	5.13	6.68	-0.87	N26°E

Table 2 Results of initial horizontal principal stress and stress tensors

$σ H m a x 0$ /MPa	$σ h m i n 0$ /MPa	$σ v 0$ /MPa	$σ x x 0$ /MPa	$σ y y 0$ /MPa	$τ x y 0$ /MPa	σ_Hmax方向
6.92	4.70	2.51	5.13	6.68	-0.87	N26°E

Table 3 Results of variations of stress tensors under the two-dimensional plane stress state(the first stage)

组合方案	分量	Δ⁰¹σ_xx/MPa	Δ⁰¹σ_yy/MPa	Δ⁰¹τ_xy/MPa
①	3、2、4	-0.011 3	-0.021 7	0.303 2
②	2、4、1	0.124 2	0.238 5	-0.014 1
③	4、1、3	0.187 1	0.208 3	0.110 9
④	1、3、2	0.334 8	0.603 2	-0.208 6

Table 4 Results of the principal stress in Bayi drilling hole in Nyching before Nepal earthquake

组合方案	$σ x x 1$ /MPa	$σ y y 1$ /MPa	$τ x y 1$ /MPa	$σ H m a x 1$ /MPa	$σ h 1 m i n$ /MPa	$σ v 1$ /MPa	$σ H m a x 1$ 方向
①	5.12	6.66	-0.57	6.85	4.93	2.51	NE18°
②	5.25	6.92	-0.89	7.31	4.87	2.51	NE23°
③	5.31	6.89	-0.76	7.20	5.00	2.51	NE22°
④	5.46	7.29	-1.08	7.79	4.96	2.51	NE24°

Table 4 Results of the principal stress in Bayi drilling hole in Nyching before Nepal earthquake

组合方案	$σ x x 1$ /MPa	$σ y y 1$ /MPa	$τ x y 1$ /MPa	$σ H m a x 1$ /MPa	$σ h 1 m i n$ /MPa	$σ v 1$ /MPa	$σ H m a x 1$ 方向
①	5.12	6.66	-0.57	6.85	4.93	2.51	NE18°
②	5.25	6.92	-0.89	7.31	4.87	2.51	NE23°
③	5.31	6.89	-0.76	7.20	5.00	2.51	NE22°
④	5.46	7.29	-1.08	7.79	4.96	2.51	NE24°

Table 5 Results of variations of stress tensors under the two-dimensional plane stress state(the second stage)

组合方案	分量	Δ⁰²σ_xx/MPa	Δ⁰²σ_yy/MPa	Δ⁰²τ_xy/MPa
①	3、2、4	-0.055 5	0.109 7	0.094 5
②	2、4、1	0.105 4	0.164 4	0.012 6
③	4、1、3	0.198 7	0.093 2	0.128 0
④	1、3、2	0.285 6	0.422 8	-0.132 6

Table 6 Results of principal stress of coseismic monitoring with Nepal earthquake in Bayi drilling hole in Nyching

组合方案	$σ x x 2$ /MPa	$σ y y 2$ /MPa	$τ x y 2$ /MPa	$σ H m a x 2$ /MPa	$σ h m i n 2$ /MPa	$σ v 2$ /MPa	$σ H m a x 2$ 方向
①	5.07	6.79	-0.78	7.10	4.77	2.51	NE21°
②	5.23	6.85	-0.86	7.22	4.86	2.51	NE23°
③	5.33	6.78	-0.75	7.09	5.01	2.51	NE22°
④	5.41	7.11	-1.01	7.58	4.94	2.51	NE25°

Table 6 Results of principal stress of coseismic monitoring with Nepal earthquake in Bayi drilling hole in Nyching

组合方案	$σ x x 2$ /MPa	$σ y y 2$ /MPa	$τ x y 2$ /MPa	$σ H m a x 2$ /MPa	$σ h m i n 2$ /MPa	$σ v 2$ /MPa	$σ H m a x 2$ 方向
①	5.07	6.79	-0.78	7.10	4.77	2.51	NE21°
②	5.23	6.85	-0.86	7.22	4.86	2.51	NE23°
③	5.33	6.78	-0.75	7.09	5.01	2.51	NE22°
④	5.41	7.11	-1.01	7.58	4.94	2.51	NE25°

Table 7 Results of variations of stress tensors under the two-dimensional plane stress state(the third stage)

组合方案	分量	Δ⁰³σ_xx/MPa	Δ⁰³σ_yy/MPa	Δ⁰³τ_xy/MPa
①	3、2、4	-0.113 5	0.062 8	0.141 5
②	2、4、1	-0.005 0	0.179 6	0.049 8
③	4、1、3	0.159 4	0.049 8	0.214 0
④	1、3、2	0.370 0	0.479 6	-0.109 5

Table 8 Results of the monitoring principal stress in Bayi drilling hole in Nyching after Nepal earthquake

组合方案	$σ x x 3$ /MPa	$σ y y 3$ /MPa	$τ x y 3$ /MPa	$σ H m a x 3$ /MPa	$σ h m i n 3$ /MPa	$σ v 3$ /MPa	$σ H m a x 3$ 方向
①	5.01	6.75	-0.73	7.02	4.74	2.51	NE20°
②	5.12	6.86	-0.82	7.19	4.79	2.51	NE22°
③	5.29	6.73	-0.66	6.99	5.03	2.51	NE21°
④	5.50	7.16	-0.98	7.62	5.04	2.51	NE24°

Table 8 Results of the monitoring principal stress in Bayi drilling hole in Nyching after Nepal earthquake

组合方案	$σ x x 3$ /MPa	$σ y y 3$ /MPa	$τ x y 3$ /MPa	$σ H m a x 3$ /MPa	$σ h m i n 3$ /MPa	$σ v 3$ /MPa	$σ H m a x 3$ 方向
①	5.01	6.75	-0.73	7.02	4.74	2.51	NE20°
②	5.12	6.86	-0.82	7.19	4.79	2.51	NE22°
③	5.29	6.73	-0.66	6.99	5.03	2.51	NE21°
④	5.50	7.16	-0.98	7.62	5.04	2.51	NE24°

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