Houston, TX | May 2, 2012 Finding blind faults using ground roll reflection Craig Hyslop Robert Stewart

Outline Purpose Process Synthetics Field data Conclusions 2

Purpose 3 (Engelkemeir, 2006) Identification of blind faults – Depth: 0-50m Exploration – Depth: 0-500m Long Point Fault, Houston TX 500m

Ground roll reflection 4

A horizontal SP 5 Boundary 1 Boundary 2 distance time FlattenedEnhancedSubtracted Deconvolved Flattened/Stacked Shot record

A horizontal SP 6 Boundary 1 Boundary 2 distance time FlattenedEnhancedSubtracted Deconvolved Flattened/Stacked Free surface Shot record

Compressing dispersive wave 7 Rel. amplitude Time MASW Velocity (m/s)

Model z x Imaging Form Common Surface Location Gather – Width of the corridor stack t’ x Flattened, incoming shots

Model t’ x Imaging Form Common Surface Location Gather – Width of the corridor stack Fourier transform Mean of amplitude spectrum at each location z x Flattened, incoming shots

Synthetic, two faults 10 Model – 2000m wide m spacing: 250m -1750m m spacing: 250m-1750m - central frequency – 6Hz 700m/s600m/s 500m/s 300m/s

Synthetic, two faults 11 Higher frequencies are reflected from the shallow fault 700m/s600m/s 500m/s 300m/s

Synthetic, two faults 12 Dispersion curve used to convert to depth 700m/s600m/s 500m/s 300m/s

Field areas 13 (Engelkemeir, 2006) Hockley Fault Friendswood

14 Line 104 Geophones Vert. Vib CPT * + Equipment 120 2D 1ms Sources Vertical Vib (45000 Cone Penetrometer (0-30m)

Friendswood: shot record 15

Friendswood: processed 16 CPT is measure of shear wave velocity Map represents lateral amount of change in shear modulus Note jump in CPT at 335m

Hockley fault 17 Equipment ms Sources Vertical Cracks on road reported Premium Outlet Mall Hockley fault zone Imagery Microsoft – available exclusively through DigitalGlobe

Hockley fault: shot record 18

Hockley fault: processed 19 Location of fault indicated with dashed red line Location of cracks on road indicated by red lines at top

Hockley fault: brute stack 20

Conclusions 21 Unique reflectivity spectrum for differing depths of blind faults can be recovered from ground roll. Processed Friendswood 2D line correlates with CPT data. Processed 2D line over Hockley fault relates to crack locations and brute stack.

Aknowledgements ExxonMobil for use of data from the Friendswood Test Facility 22

Thank you 23