Subsurface Fault and Colluvial Wedge Detection Using Resistivity, Refraction Tomography and

Seismic Reflection

Sherif HanafyKing Abdullah University of science and Technology (KAUST)

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

1.Demonstrate the capability of geophysics to detect

shallow subsurface faults

2.Is Qademah fault exists?

3.Track the Qademah fault (if exist)

4.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

MethodologyGround surface

Depth

𝑡=∑𝑗=1

𝑁 𝑗

𝑥 𝑗 𝑠 𝑗 𝑡𝑖=∑𝑗=1

𝑁 𝑗

𝑥𝑖𝑗 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

KAUST

Qadema Fault

Study Area

Data Acquisition (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 AcquisationResistivity

Equipment: Syscal R2No. of Profiles: 2No. of Nodes: 64Node Interval: 5 m Profile Length: 315 mArray Type: Wenner

Seismic

Equipment: Geometrics (NZXP + Geode)No of Profiles: 1No. of shots: 109Shot Interval: 3 mNo. of Receivers: 109Receiver Interval: 3 mProfile Length: 324 m

Outline

• Motivations

• Study Area

• Data Acquisition (Resistivity and Seismic)

• Data Processing and Interpretation

• Resistivity

• Seismic

• Summary and Future Work

Resistivity ResultsSite # 1

Raw DataNo. of Nodes: 64Node Interval: 5 m Profile Length: 315 mArray Type: Wenner

Resistivity ResultsSite # 1

Inverted Data

S Sabkha CW Colluvial WedgeF Fan SG Sand-silt-gravelLS Limestone

Resistivity ResultsSite # 2

Raw DataNo. of Nodes: 64Node Interval: 5 m Profile Length: 315 mArray Type: Wenner

Resistivity ResultsSite # 2

Inverted Data

S Sabkha CW Colluvial WedgeF Fan SG Sand-silt-gravelLS Limestone

Outline

• Motivations

• Study Area

• Data Acquisition (Resistivity and Seismic)

• Data Processing and Interpretation

• Resistivity

• Seismic

• Summary and Future Work

No. of shots: 109Shot Interval: 3 mNo. of Receivers: 109Receiver Interval: 3 mProfile Length: 324 m

CSG # 600

0.250 324

X (m)

Tim

e (s

)Common Shot Gather

No of TT: 11881TT passes Reci. Test: 9488 No. of TT rejected: 2393No. 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