Imaging Normal Faults in Alluvial fans using Geophysical Techniques: Field Example from the Coast of Aqaba, Saudi Arabia Sherif M. Hanafy 28 October 2014

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Motivation Can we locate and characterize faults in alluvial sediments? We used seismic traveltime tomography and 2D resistivity imaging to locate the fault

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Study Area Red Sea Gulf of Aqaba

Study Area Fault raptured at the 1995 earthquake Seismic/resistivity profile

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Data Acquisition Seismic Data – One profile – 120 shot gather, 120 receiver/shot gather – 2.5 m shot/receiver interval – m profile length – stacks/shot location – Source is a 200 lb weight drop Resistivity – 64 Nodes – 5 m node interval – 315 m profile length – Wenner-Schlumberger configuration

Data Acquisition Fault rupture due to 1995 earthquake. Photo taken on Nov Another location of the fault rapture due to 1995 earthquake. Photo taken on Nov. 2013

Data Acquisition A photo shows the seismic and resistivity acquisition Seismic profile Resistivity profile Source: 200 lb weight drop

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Seismic Data Common Shot Gather # Time (s) Offset (m) First arrival traveltimes

Traveltime Picks Source No Receiver No. Raw Picking Source No Receiver No. After Reciprocity Time (ms) 0 210

RMS Error RMS error (ms) Itr. No.

Seismic Tomogram First arrival traveltime picks are inverted to get the traveltime tomogram The 1995 fault Colluvial Wedge Unidentified Anomaly A possible fault A possible Colluvial Wedge

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Resistivity The Res2DInv software is used to invert the resistivity data 0 45 Z (m) 0315 X (m) Resistivity (Ohm.m) 1 500

Seismic - Resistivity The 1995 fault Colluvial Wedge Unidentified Anomaly A possible fault A possible Colluvial Wedge 0 45 Z (m) 0315 X (m) Resistivity (Ohm.m) 1 500

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Conclusions Seismic and resistivity methods can be used to locate hidden faults in the subsurface. One example is collected at the Gulf of Aqaba coast. Results show the location of fault due to the 1995 earthquake. Possible local anomalies are shown on the traveltime tomogram and the 2D resistivity image. Further study is required to explain the nature of these local anomalies

Outline Motivation: Faults in alluvial sediments Study Area: Gulf of Aqaba Data Acquisition: Seismic and resistivity Seismic Result: Traveltime tomography Resistivity Result: 2D imaging Conclusions Future Work

Seismic reflection processing to generate the zero-stacked section. Use the traveltime tomogram to migrate the data Common Shot Gather # Time (s) Offset (m)

Acknowledgements I would like to thank The CSIM sponsors for their support The the students of the “Geophysical Field Methods” class for their help in data collection Thank You