Subsurface mapping by ambient noise tomography

Title: Subsurface Mapping by Ambient Noise Tomography (Brief Introduction) 1. Understanding subsurface (lithology, structure...): important in several discipline: geotechnical engineering, volcanology, geomorphology, civil engineering, economic geology... 2. Drilling borehole: traditional method, but invasive 3. Geophysical survey: non-invasive method to image the subsurface 4. Example of geophysical survey technique: electrical resistivity, gravity anomaly, seismic 5. Use of ambient noise: raising usage and thus attention

Draft 1 Ambient noise, one of the seismic waves, is the background noise produced by various natural and human activities. Recently scientists, especially seismologists, discover the potential of ambient noise on subsurface structure mapping. Borehole drilling is considered as the most ordinary method to understand the subsurface lithology, but it is invasive. Geophysical survey acts as an alternative non-invasive measure on the exploration of subsurface structure. Some of the main survey technique include electrical resistivity, gravity anomaly and seismic. Comparing with other geophysical survey technique, measuring ambient noise becomes a rising star.

Part 1: Source of Ambient Noise 1. Brief classification of seismic source

  1.1 Type of seismic waves
  1.2 Frequency range of ambient noise

2. Nature of ambient noise: passive/background noise

  2.1 Active/Artificial Noise
  2.2 Passive/Natural Noise

3. Variation of Ambient Noise

  3.1 Cause of variation
  3.2 Periodic change of ambient noise

4. Difficulty in collecting ambient noise

Draft 1 Seismic wave can be classified into P-wave, S-wave, Rayleigh wave and love wave. The latter 2 types are surface waves.

Part 2: Seismic Velocity Structure Modelling 1. Data collection method

  1.1 Tools of collection
  1.2 Available online source

2. Theory of ambient noise correlation

  2.1 cross correlation
  2.2 green's function
  2.3 Inversion

3. Subsurface structure correlation with velocity imaging

  3.1 example of subsurface structure
  3.2 linkage of structure with velocity zone
     3.2.1 low-velocity zone
     3.2.2 high-velocity zone

Part 3: Application of Subsurface Mapping 1. Exploration of underground mines 2. Volcano Monitoring 3. Landslide Monitoring