4.2　Geological Investigation

4.2.1　The regional geologic structure investigation shall cover the following:

1　Collecting and sorting-out geologic structure data，dividing main geotectonic units，analyzing the evolution characteristics of the regional geologic structure，fault structure and their development features，and preparing regional geologic structure map.

2　Collecting and sorting-out new tectonic data of the region，analyzing the basic features of regional strata and geomorphic development since the Neogene period，the geodynamic background，new tectonic movement and basic features of current crustal deformation，preparing new tectonic zonation map，indicating the characteristics of new tectonic zones and describing the features of the new tectonic zone where the site is located.

3　Collecting and sorting-out the distribution and scale，activity nature，activity era，activity strength，activity period division and relevant quantitative data of main faults，assessing the activity of main faults and determining their closest distance to the site.

4　When there is Quaternary volcanic activity in the region，its latest activity era，activity type and features shall be investigated to preliminarily assess if the volcanic activity will affect the site qualification.

5　Collecting regional gravity，aero-magnetic and other geophysical field data，analyzing the geophysical field feature and its relation with earthquake；preparing Bouguer gravity anomaly，aeromagnetic anomaly and crust thickness map.

4.2.2　When there may be seismogenic structure with significant impact to site evaluation in the region，and the existing information is insufficient for a preliminary evaluation of its activity and its effect on site，field investigation shall be conducted.

4.2.3　The geologic structure investigation in near region shall cover the following:

1　Collecting and sorting-out geologic structure data to indicate the basic features of the near region geologic structure；preparing near region geologic structure map.

2　Collecting and sorting-out data on neotectonic movement and current crust deformation，and briefly analyzing geotectonic development and activity features.

3　Analyzing and interpreting remote sensing image data，and necessary investigation shall be conducted when any image of possible active fault is identified.

4　Investigating and identifying activity of main faults，which should include fault scale，activity era，nature，movement characteristics and period division features，and maps of original data for identifying the activity of main faults shall be prepared.

5　Analyzing activity features of main faults，and preparing a list and activity distribution maps of main faults.

4.2.4　When there is possible seismogenic structure that may affect site qualification in the coverage of quaternary strata and water area，preliminary survey shall be performed with suitable geophysical exploration method，and the suitability of the method used shall be demonstrated.In the interpretation of geophysical survey data，data that can indicate the thickness，stratification and era of the quaternary strata shall be fully collected，to reasonably interpret the geophysical exploration profile，and when necessary，geological exploratory trench，drilling and age-dating shall be conducted.