Passive low frequency seismic (lfs) system and method to detect and image subsurface search objects and fluid properties

A system for detecting and imaging subsurface search objects, the system comprising:

• a plurality of sensors for recording microseismic signals in a predetermined area;
• a processing module configured to process microseismic signals including by:
• filtering noise in the recorded microseismic signals associated with a correlated horizontal wave component from a vertical wave component;
• filtering a narrowband harmonic component of the recorded microseismic signals;
• retrieving the vertically propagating waves from the microseismic ambient background in the recorded microseismic signals including by:
• excluding broadband interference from the microseismic ambient background wave field;
• accumulation of the tensor of cross-correlation functions;
• suppressing the scattered component of the Rayleigh surface wave using the tensor of the cross-correlation functions;
• and
• performing final filtering on the collection of cross-correlation functions to exclude an inclined component in the gathering of cross-correlation functions;
• a simulation module configured to:
• model the expected vertical component in the predetermined area by way of a seismic simulation that enables the propagation of seismic waves in a multiphase medium, wherein the modeling is based on prior data for the predetermined area, including vertical seismic profile, depth and time maps, or elevation data;
• and
• generate a predicted subsurface earth structure by comparing the recorded, processed microseismic signals to the modeled expected vertical component in the predetermined area.

A method for detecting and imaging subsurface search objects, the method comprising:

• processing recorded microseismic signals comprising waves with a vertical component and a horizontal component collected in a predetermined area including by:
• filtering noise in the recorded microseismic signals associated with a correlated horizontal wave component from the vertical wave component;
• filtering a narrowband harmonic component of the recorded microseismic signals;
• retrieving the vertically propagating waves from the microseismic ambient background in the recorded microseismic signals including by:
• excluding broadband interference from the microseismic ambient background wave field;
• accumulation of the tensor of cross-correlation functions;
• suppressing the scattered component of the Rayleigh surface wave using the tensor of the cross-correlation functions;
• and
• performing final filtering on the collection of cross-correlation functions to exclude an inclined component in the gathering of cross-correlation functions;
• modeling the expected vertical component in the predetermined area by way of a seismic simulation that enables the propagation of seismic waves in a multiphase medium, wherein the modeling is based on prior data for the predetermined area, including vertical seismic profile, depth and time maps, or elevation data;
• and
• generating a predicted subsurface earth structure by comparing the recorded, processed microseismic signals to the modeled expected vertical component in the predetermined area.