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DBT81-2020: Active fault survey - Paleoseismic trenching
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Active fault survey - Paleoseismic trenching
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DB/T 81-2020
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Basic data | Standard ID | DB/T 81-2020 (DB/T81-2020) | | Description (Translated English) | Active fault survey - Paleoseismic trenching | | Sector / Industry | Chinese Industry Standard (Recommended) | | Classification of Chinese Standard | P15 | | Classification of International Standard | 91.120.25 | | Word Count Estimation | 36,347 | | Date of Issue | 2020 | | Date of Implementation | 2020-07-01 | | Issuing agency(ies) | China Earthquake Administration | DBT81-2020: Active fault survey - Paleoseismic trenching---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
(Exploration of active faults)
ICS 91.120.25P15
People's Republic of China Earthquake Industry Standard
Active fault exploration ancient seismic trough exploration
Released on 2020-03-30
Implementation of 2020-07-01
Issued by China Earthquake Administration
Table of contents
Preface Ⅲ
Introduction Ⅳ
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Work process 2
5 Preliminary preparation 4
6 Location selection 4
7 Topographic mapping and trench excavation 5
8 Preparation of the groove record 6
9 Interpretation of exploration trenches and paleoearthquake identification 6
10 Sampling and dating 7
11.Ancient earthquake identification mark 9
12 Outcomes 10
Appendix A (informative appendix) Example of trough location 11
Appendix B (Informative Appendix) Trench Excavation and Record 16
Appendix C (Normative Appendix) Test Method for Analysis Results of Ancient Earthquake Events 19
Appendix D (Normative Appendix) Limiting methods for determining the age of ancient earthquake events 22
Appendix E (informative appendix) Paleoearthquake recognition model and example results 24
References 31
Foreword
This standard is one of the series of standards for "Active Fault Exploration". The standard structure and name of the series are expected to be as follows.
---Remote sensing survey for active fault detection (DB/T 69-2017);
--- Active fault exploration field geological survey (DB/T 82-2020);
--- Active fault exploration and fault geomorphological survey (DB/T 71-2018);
---Active fault exploration, ancient seismic trench exploration (DB/T 81-2020);
---Active fault exploration and drilling;
---Dating test of active fault exploration;
---Active fault exploration and seismic exploration;
---Activity identification of active fault exploration;
---Evaluation of seismic hazard of active fault exploration;
---Graphic symbols for active fault exploration (DB/T 72-2018);
---Active fault exploration database;
---Active fault exploration database detection (DB/T 83-2020);
---Active fault exploration 1.25,000 seismic structure map compilation (DB/T 73-2018);
---Report on the results of active fault exploration;
--- 1.5000 active fault mapping (DB/T 53-2013);
--- 1.5000 active fault mapping database specification (DB/T 65-2016);
This standard was drafted in accordance with the rules given in GB/T 1.1-2009 "Guidelines for Standardization Work Part 1.Standard Structure and Compilation".
This standard was proposed by the China Earthquake Administration.
This standard is under the jurisdiction of the Earthquake Disaster Prevention Standardization Technical Committee.
Drafting organizations of this standard. Institute of Geology, China Earthquake Administration, Institute of Crustal Stress, China Earthquake Disaster Prevention Center,
Institute of Earthquake Prediction, China Earthquake Administration, Seismological Bureau of Ningxia Hui Autonomous Region.
The main drafters of this standard. Ran Yongkang, Xu Xiwei, Wang Hu, Chai Chizhang, Yu Guihua, Yang Xiaoping, He Honglin, Leng Wei, Wu Xiyan, Liu Huaguo,
Gao Shuaibo.
National Earthquake Disaster Prevention Center; Zip Code. 100029), and indicate the contact information.
Introduction
Numerous site surveys of major earthquakes at home and abroad and analysis of their disaster phenomena show that active faults are the source of earthquakes and also earthquake disasters.
The culprit. Finding out the exact location of seismically active faults and making scientific evaluations of their attributes and seismic risk is an earthquake disaster risk assessment
And the important basic work of earthquake disaster prevention. Since the "Eighth Five-Year Plan" period, my country has gradually promoted the detection of active faults.
Great progress has been made in urban planning, land use, and engineering construction. Some practical experience has been accumulated.
And earthquake science research and other fields have played an important role.
In recent years, the seismic department has organized and carried out active fault detection technology to sort out the work process, work content and work results.
This framework. In order to standardize and guide our country’s active fault detection work and its application, the GB/T 3602-2018 "Active Fault
Layer detection", the standard provides technical requirements for active fault detection in terms of work content, workflow, technical methods, data management, and outcome output.
The requirements are stipulated. On this basis, further evaluation and analysis of various technical methods to achieve detection purposes are carried out to clarify their technical indicators and
Data collection requirements and a standard framework for active fault detection have been constructed.
Paleoseismic trench exploration is one of the main technical methods for active fault detection and location, fault activity identification and seismic risk assessment.
It has been widely used in active fault detection, active fault mapping, and active fault investigation on engineering sites. In view of the identification of trenches and ancient earthquakes
Complexity, it is necessary to standardize trenching technology and ancient seismic identification methods, and this standard is specially formulated.
Active fault exploration ancient seismic trough exploration
1 scope
This standard specifies the preliminary preparation, site selection, site excavation, sample collection, identification of paleo-seismic events and related cost
Requirements for data storage.
This standard applies to geological mapping of active faults, urban active fault detection, and paleo-seismic trough exploration in active fault identification. Ground
Earthquake scientific investigation can also be used as a reference.
2 Normative references
The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this article
Pieces. For undated references, the latest version (including all amendments) applies to this document.
GB/T 15608-2006 China Color System
DB/T 65-2016 1.5000 active fault mapping database specification
DB/T 69-2017 Active Fault Exploration Remote Sensing Survey
DB/T 71-2018 active fault exploration fault geomorphological survey
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
There have been active faults since 120,000 years ago, including Late Pleistocene faults and Holocene faults.
[GB/T 3602-2018, definition 3.1]
3.2
There have been faults, but it is difficult to identify the faults of the dislocation plane in the formation.
3.3
The amount of slip generated by an active fault during an earthquake rupture.
[GB/T 3602-2018, definition 3.13]
3.4
There are no written records of earthquake events discovered by geological methods.
[GB/T 3602-2018, definition 3.16]
3.5
A valley developed along the fault line.
4 Work process
4.1 Figure 1 shows the ancient seismic trough exploration workflow, including the following 7 stages.
a) Preliminary preparation;
b) Location selection;
c) Topographic mapping and trench excavation;
d) Preparation of groove record;
e) Exploration trench interpretation and paleo-seismic identification;
f) Sampling and dating;
g) Results and outputs.
4.2 Trench interpretation, sampling and dating, and paleoearthquake identification can be carried out simultaneously.
5 Preparation
5.1 Data collection
5.1.1 High-resolution remote sensing images of target faults, research on the activity of existing faults, and results of trench exploration work should be collected.
5.1.2 The stratum, structure, topography and climate data along the active fault at pre-selected locations and nearby areas should be collected and sorted out.
5.2 Image interpretation
5.2.1 Remote sensing images with a resolution better than 1m shall be used to determine suitable locations for trenching work, and shall be processed in accordance with the provisions of DB/T 69-2017
Line image interpretation.
5.2.2 For strike-slip faults, fault troughs, fault plug ponds, fault depression ponds, small pull-off basins, small gullies and gully beds, etc. shall be identified
Location.
5.2.3 For normal faults and reverse faults, the stratified landforms of the ascending disk of the fault and the fault ridges, and the graben and depressions in front of the fault ridges shall be identified.
To wait.
5.3 Field survey
5.3.1 Field surveys should be carried out on pre-selected locations to assess whether they meet the requirements of Chapter 6.
5.3.2 The geomorphology of the preselected site should not be artificially modified, and the impact of artificial modification should be assessed if it cannot be avoided.
5.3.3 The coseismic displacement of ancient earthquake events should be evaluated based on the interpretation results of remote sensing.
5.3.4 The structural position of the preselected location of the exploration trench along the target fault shall be evaluated.
5.4 Data storage
It shall be in accordance with Table A in DB/T 65-2016.1.Table A. 4 ~ Table A. 13.Table A. 25.Table A. 28 ~ Table A. 31 requirements are collected
The data information is merged into the database.
6 Location selection
6.1 Basic requirements
6.1.1 The location should be selected where the fault structure is simple, the accumulation is continuous, and the accumulation is clearly layered, and the dating samples can be collected.
6.1.2 The location of the exploration trough should be avoided.
a) Fault trough developed by soluble rock and seismic depression;
b) The slope of the trough is steep, and the part where coarse particulate matter accumulates at the foot of the slope;
c) Locations with frequent erosion and accumulation;
d) Areas affected by landslides and debris flows;
e) Areas with abnormal development of freezing and thawing.
6.2 Location of strike-slip fault trench
6.2.1 Pull-apart basins, fault troughs, fault plug ponds, fault depression ponds, gully beds staggered by faults, etc. should be selected, and meet the following requirements.
a) Pull-apart basins with a width of less than 100m are preferred. For large pull-apart basins, the oblique cut-off layer in the basin is preferred.
Select the boundary fault location;
b) Select a fault trough with a width of less than 150m, and select a low-lying or relatively convergent place in the trough;
c) Choosing faulty ponds and rifting ponds with a width less than 100m;
d) Select the part where the gully passes through the fault at a near vertical or large angle, and both sides are young accumulation strata;
e) The width of small gullies staggered by faults should be less than 5m.
6.2.2 Figure A in Appendix A. 1~Figure A. 4 gives four examples of location selection for strike-slip trenches.
6.3 Location of reverse fault exploration trench
6.3.1 It is advisable to choose a site with a single steep ridge, continuous accumulation in front of the ridge, and a cumulative height 2 times or more than the coseismic displacement. Choose alluvial fans,
Fault ridges on the second or third terraces of rivers, reverse ridges or depressions caused by thrusting.
6.3.2 Figure A. 5 gives an example of location selection for reverse fault trenches.
6.4 Location of normal fault trench
6.4.1 It is advisable to choose a site with a single steep ridge, continuous accumulation in front of the ridge, and a cumulative height 2 times or more than the coseismic displacement. Choose alluvial fans,
The steep ridge of the fault on the second or third terrace of the river, the part with a small graben structure.
6.4.2 Figure A. 6 gives an example of location selection for normal fault trenches.
6.5 Data storage
After the site selection is determined, it should be in accordance with Table A in DB/T 65-2016.The 40 requirements fill in the location coordinates and store them in the warehouse.
7 Topographic mapping and trench excavation
7.1 Basic requirements
7.1.1 The trench layout and excavation style should be selected according to the nature of the fault and the excavation target, and the scale of excavation should be determined. Figure B in Appendix B. 1
An example of trench excavation style is given.
7.1.2 It is advisable to take photos to record the original topography of the excavation site.
7.1.3 During the construction of the trench, when the depth of the trench is greater than 2m, supporting measures should be taken to prevent the trench from collapsing.
7.1.4 When excavating a trench with a depth greater than 3.5m, the stepped excavation method should be adopted, the step width should be 1m, and the step height difference should be 1.7m~
2.3m.
7.2 Topographic surveying and mapping
7.2.1 Before excavation of the trench, it is advisable to carry out the faulty geomorphological survey near the location of the trench in accordance with the regulations of DB/T 71-2018.
7.2.2 The range of topographic surveying and mapping shall cover the exploration trench and nearby structural deformation geomorphology.
7.3 Excavation of trench
7.3.1 Strike-slip fault
7.3.1.1 It is advisable to first excavate a trench that spans the entire fault zone, and then, according to the exposed fault position, be perpendicular or parallel to the excavation combination of the fault.
Probe groove. Figure B in Appendix B. 2 gives an example of plan layout and excavation of strike-slip fault trench.
7.3.1.2 The stratum and structural information can be exposed by stripping the trench wall layer by layer.
7.3.1.3 Where there are no conditions for excavation of combined trenches, two or more vertical fault trenches should be laid.
7.3.1.4 The depth of the trench should not be less than 2.5m, and the width of the bottom of the trench should be greater than 1.5m.
7.3.2 Reverse fault
7.3.2.1 A vertical fault should be laid and a trench that spans the entire surface rupture zone of the Late Quaternary, and a location with a complex topography or accumulation pattern in front of the ridge
It is advisable to lay a combined trough. Figure B. 3 gives an example of the plane layout and excavation of a reverse fault trench.
7.3.2.2 The depth of the trench should be more than twice the co-seismic displacement, and the bottom width of the trench should be greater than 1.5m.
7.3.2.3 Excavation of the ascending disk should be able to control the surface rupture zone of the Late Quaternary, the length should account for 3/5 of the length of the entire trench, and the descending disk should be fully exposed
Accumulation of slope belt in front of ridge.
7.3.3 Normal fault
7.3.3.1 A vertical fault should be laid out and a trench that spans the entire Late Quaternary surface rupture zone, where there are graben and other complex structures in front of the ridge can be deployed
Set up a combined probe. Figure B. 4 gives an example of the layout and excavation of a normal fault trench.
7.3.3.2 The depth of the trench should be more than twice the co-seismic displacement, and the bottom width of the trench should be greater than 1.5m.
7.3.3.3 The excavation length of the descending plate should account for 2/3 of the entire length of the trench.
7.4 Data storage
It shall be in accordance with Table A in DB/T 65-2016.40.Table A. 45 ~ Table A. The requirement of 50 summarizes the topographic surveying and mapping data of the excavation point and the trench gauge
The mold parameters are merged into the library.
8 Preparation of groove record
8.1 Trough trimming
The trough should be repaired and meet the following requirements.
a) Clean the walls of the trench first to ensure that it is level and free of floating soil coverage, and the stratum boundaries and structural signs are clear;
b) The sand layer should be leveled, and excavation scratches and other artificial marks should be removed;
c) The gravel layer should be basically flat.
8.2 Trench mark
Different color labels should be used to mark on the wall of the trough. The information to be marked includes.
a) Signs of fault activity such as fault traces, stratum deformation and structural wedge;
b) Special sedimentary strata such as marker strata, buried soil, collapse wedge and filling wedge;
c) Sample location, fossils or special deposits, such as animal hair, volcanic ash, baking layer, mineral nodules or rich accumulation layer and other dating materials
Location.
8.3 Network building imaging
8.3.1 A 1m×1m reference grid coordinate should be established.
8.3.2 The orthographic image of the trench wall shall be made in one of the following ways.
a) Take photos with grid as the unit, and the overlapping area of adjacent photos is not less than 20%; the optical axis of the camera should be perpendicular to the surface of the groove, and the light should be selected.
Take pictures when the line is stable and soft; do ortho-correction and stitching of the photos to make an orthographic image of the trench wall;
b) Use other technical methods to obtain orthographic images of the trench wall.
9 Interpretation of exploration trenches and paleo-seismic identification
9.1 Preliminary interpretation
9.1.1 Faults should be marked on the trench wall.
9.1.2 According to sedimentary unconformities, changes in the accumulation environment, such as grain size, color mutation and other phenomena, preliminary division and identification of stratigraphic units, piles
Accumulate the order, and analyze the causes of each level unit.
9.1.3 The ancient earthquakes shall be identified, marked and described in accordance with the provisions of Chapter 11.
9.2 Probe record
9.2.1 The stratigraphic unit should be outlined on the orthophoto of the trench wall, and information such as genetic type, structural deformation and paleo-seismic event layer, samples and fossils, and special deposits should be marked to form an interpretation map of the trench profile. Figure B. 5 gives an example of a groove record.
9.2.2 The trough information shall be described in accordance with the following requirements.
a) Describe the stratum color in accordance with the color code of the color system specified in GB/T 15608-2006;
b) Use gravel, coarse sand-medium sand-fine sand-silt sand, clay-peat, bedrock-bedrock weathering, etc. to classify formation materials;
c) Describe the roundness, sortability and particle size of gravel;
d) Analyze the genetic types and bedding development of accumulative stratigraphic units;
e) Describe the characteristics of the formation phase transition, collapse wedge and packing wedge accumulation;
f) Describe whether there is local angular unconformity contact between the stratigraphic units;
g) Describe whether there are fossils, mineral nodules or accumulations in the formation;
h) Describe the paleosol layer and its degree of development;
i) Describe the signs of deformation such as faults, joints, cracks, folds, and sand liquefaction.
9.2.3 The local directional characteristics of fine-grained materials and the local looseness of coarse-grained materials should be observed, or the directional sampling grinding piece should be used to test the hyperspectral and magnetic properties.
Determine whether there is a hidden fault and its location based on the physical properties of the formation such as the rate of conversion.
9.3 Confirmation of ancient earthquake events
9.3.1 The interpretation map and written record information of the trough section shall be checked on site, and the ancient earthquake events shall be analyzed and confirmed.
9.3.2 The authenticity of the analysis results of ancient earthquake events shall be verified in accordance with the method specified in Appendix C. Applications that cannot meet the inspection requirements
Re-identify, record and interpret at the scene, re-analyze the results, and then verify the authenticity of the ancient seismic event analysis results until the test results
So far.
9.3.3 Field records, photos and drawings of paper media and electronic files shall be kept at the same time.
9.4 Data storage
It shall be in accordance with Table A in DB/T 65-2016.40 and Table A. According to the requirements of 41, the map and text data of the field interpretation results shall be collected and stored.
10 Sampling and dating
10.1 Basic requirements
10.1.1 The stratum exposed by the exploration trench should be collected layer by layer to determine the age samples of the paleo-seismic event; when there is no condition for layer-by-layer sampling, it should be based on the characteristics of the post-earthquake accumulation strata of different faults to affect the strata and post-earthquake overlay Take a sample.
10.1.2 The collection of samples should be carried out in accordance with the requirements of the relevant chronology laboratory to avoid sample contamination and interference.
10.1.3 The collection of carbon fourteen (14C) samples should start when the trench is trimmed.
10.1.4 The sampling location should avoid fault deformation zone and strata boundary.
10.1.5 Sampling at the location of collapse wedge and filling wedge should avoid mixed accumulation and clumps.
10.1.6 The sampling point and the sample storage container should be marked and photographed at the same time.
10.1.7 The position and label of the sample should be marked during the field trench record.
10.1.8 The carbon fourteen dating method should be used first, followed by luminescence (TL+OSL), cosmogenic nuclides (TCN) and other dating methods
method.
10.1.9 The rationality of the dating results of serial samples should be analyzed, and invalid samples such as contaminated and re-transported samples should be eliminated.
10.1.1.10 The age of carbon fourteen samples should be corrected by chronological data. You can refer to and use "Key Technologies and Case Analysis of Ancient Seismic Research in Mainland China (4) ---Sample Collection and Event Years of Ancient Seismic Dating Techniques"
The correction method given in "Generation Analysis".
10.1.111 The time limit of ancient earthquakes should be given interval values.
10.2 Sequence sample collection
10.2.1 When the thickness of the stratigraphic unit is less than 30 cm, the amount of C14 samples collected in each layer should be no less than two.
10.2.2 When the thickness of the stratigraphic unit is 30 cm to 50 cm, the amount of C14 samples collected in each layer should be no less than 3, preferably near the upper part of the strata.
Collect 2 luminescence samples at the lower and lower positions.
10.2.3 When the thickness of the stratigraphic unit is 50 cm to 100 cm, the amount of C14 samples collected in each layer should be no less than 4, and it should be in the upper and middle of the strata.
Two luminescence samples were collected from the lower part and the lower part.
10.2.4 When the thickness of the stratum unit is greater than 100 cm, the amount of C14 samples collected in each layer should be no less than 5, and the sampling interval of luminescence samples should be
Less than 40cm.
10.3 Single event collection
10.3.1 Strike-slip fault
10.3.1.1 When the fault signs are clear and the relationship between stratigraphic coverage and cutting is clear, it should be in the surface strata and paleo-earthquake at the time of the paleo-seismic event.
The oldest strata accumulated after the event were sampled separately.
10.3.1.2 When the fault signs are not clear or the invisible fault is difficult to define the paleo-seismic event layer, the level and quantity of sample collection should be increased.
10.3.2 Reverse fault
10.3.2.1 Sampling should be done in the lower part of the growth strata and the upper part of the collapse wedge (that is, where the slab flow forms the slope deposit) to define the latest age of the paleo-seismic event.
10.3.2.2 Sampling should be taken from the young strata where the footwall of the fault was broken or deformed (that is, the surface layer at the time of the paleo-seismic event) to limit paleo-earthquakes.
The earliest age of the event.
10.3.3 Normal fault
10.3.3.1 Sampling should be taken at the upper part of the collapse wedge (that is, the part where the flowing water forms the slope deposit) to define the latest age of the paleo-seismic event.
10.3.3.2 Sampling should be made on the young strata where the hanging wall of the fault was broken or deformed (that is, the surface layer at the time of the paleo-seismic event) to limit the paleo-earthquake
The earliest age of the event.
10.4 On-site sampling requirements
10.4.1 Carbon fourteen sample
The collection of carbon fourteen samples shall meet the following requirements.
a) Prioritize the collection of seeds, leaves, small branches, bark, animal hair, charcoal, peat, sandy soil r...
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