Inverting Resistivity and Seismic Data to Find Subsurface Faults Sherif Hanafy King Abdullah University of science and Technology (KAUST) The 6th International Conference “Inverse Problem and Simulation” 23 May 2012

Outline Motivations Methodology Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Outline Motivations Methodology Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Motivations Demonstrate the capability of geophysics to detect shallow subsurface faults Is Qademah fault exists? Track the Qademah fault (if exist) trenching and dating ancient earthquakes at Qademah fault to assess size and recurrence intervals

Outline Motivations Methodology Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Methodology Ground surface Depth 𝑡= 𝑗=1 𝑁 𝑗 𝑥 𝑗 𝑠 𝑗 𝑡= 𝑗=1 𝑁 𝑗 𝑥 𝑗 𝑠 𝑗 𝑡 𝑖 = 𝑗=1 𝑁 𝑗 𝑥 𝑖𝑗 𝑠 𝑗 t’s are known, x’s are know, and s’s are unknown

Outline Motivations Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Study Area KAUST Qadema Fault

(Resistivity and Seismic) Data Acquisition (Resistivity and Seismic)

(Resistivity and Seismic) Data Acquisition (Resistivity and Seismic)

Topography

Outline Motivations Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Data Acquisation Seismic Resistivity Equipment: Geometrics (NZXP + Geode) No of Profiles: 1 No. of shots: 109 Shot Interval: 3 m No. of Receivers: 109 Receiver Interval: 3 m Profile Length: 324 m Resistivity Equipment: Syscal R2 No. of Profiles: 2 No. of Nodes: 64 Node Interval: 5 m Profile Length: 315 m Array Type: Wenner

Outline Motivations Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Resistivity Results Site # 1 No. of Nodes: 64 Node Interval: 5 m Profile Length: 315 m Array Type: Wenner Raw Data

Resistivity Results Site # 1 S Sabkha CW Colluvial Wedge F Fan SG Sand-silt-gravel LS Limestone Inverted Data

Resistivity Results Site # 2 No. of Nodes: 64 Node Interval: 5 m Profile Length: 315 m Array Type: Wenner Raw Data

Resistivity Results Site # 2 S Sabkha CW Colluvial Wedge F Fan SG Sand-silt-gravel LS Limestone Inverted Data

Outline Motivations Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Common Shot Gather CSG # 60 Time (s) X (m) No. of shots: 109 0.25 324 X (m) Time (s) No. of shots: 109 Shot Interval: 3 m No. of Receivers: 109 Receiver Interval: 3 m Profile Length: 324 m No of TT: 11881 TT passes Reci. Test: 9488 No. of TT rejected: 2393 No. of Iterations: 40

Refraction Tomogram

Reflection Stacked Section

Reflection Stacked Section

Result Summary

Outline Motivations Study Area Data Acquisition (Resistivity and Seismic) Data Processing and Interpretation Resistivity Seismic Summary and Future Work

Summary and Future Work Resistivity and seismic methods used to detect the Qademah fault One colluvial wedge is shown on both ERT and refraction tomogram Reflection stacked section shows the Qademah fault and the associated antithetic fault(s)

Summary and Future Work The Qademah Fault will be tracked to the south with Seismic Resistivity EM and possibly GPR A trench will be made at Qademah fault to date the colluvial wedge If more than one colluvial wedge is found, then we will be able to find the fault recurrence.

Thank You