Wide Area Seismic Detection

• US 20110069302A1
• Filed: 09/16/2010
• Published: 03/24/2011
• Est. Priority Date: 09/18/2009
• Status: Active Grant

• Current Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Hill, David John, McEwen-King, Magnus
• Granted Patent: US 9,435,902 B2
• Time in Patent Office: Days
• US Class Current: 356/73.1
• CPC Class Codes: G01D 5/35361 using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G01V 1/001 Acoustic presence detection
• CPC Class Codes: G01V 1/003 Seismic data acquisition in general, e.g. survey design G01V1/3808, G01V1/42 take precedence
• CPC Class Codes: G01V 1/01 Measuring or predicting earthquakes
• CPC Class Codes: G01V 1/186 Hydrophones

Abstract

A method for monitoring for seismic events by interrogating an optic fibre which forms part of an existing communications infrastructure to provide distributed acoustic sensing (DAS). The signals provided by the distributed sensing provide measurements at each of a plurality of discrete portions along the fibre, which may be many tens of kilometres in length. Warning or measurement and consequently prediction of seismic activity can be provided by collecting data over a wide area, without the need to deploy a correspondingly large fibre network.

Claims

1. A method of monitoring for seismic events comprising interrogating at least one optical fibre within a communications infrastructure with optical pulses so as to provide at least one optical fibre distributed acoustic sensor and monitoring the signal from said at least one distributed acoustic sensor for seismic activity.

2. A method as claimed in claim 1 wherein the step of interrogating the at least one optical fibre with optical pulses so as to provide at least one optical fibre distributed acoustic sensor comprises the steps of, for the or each fibre:

launching a series of optical pulses into said fibre and detecting radiation Rayleigh backscattered by the fibre; and

processing the detected Rayleigh backscattered radiation to provide a plurality of discrete longitudinal sensing portions of the fibre.

3. A method as claimed in claim 1 wherein said at least one optical fibre distributed acoustic sensor is arranged to provide wide area monitoring for large scale seismic events.

4. A method as claimed in claim 1 comprising providing a plurality of optical fibre distributed acoustic sensors.

5. A method as claimed in claim 4 wherein the optical fibres within said communication infrastructure that are provided as optical fibre distributed acoustic sensors comprise at least one fibre configured such that at least part of said fibre runs in a different direction to at least part of another fibre.

6. A method as claimed in claim 4 further comprising the step of interrogating at least one optical fibre which is arranged in a location solely for the purposes of distributed acoustic sensing with optical pulses so as to provide at least one optical fibre distributed acoustic sensor.

7. A method as claimed in claim 1 wherein the step of monitoring the signal from said at least one distributed acoustic sensor for seismic activity comprises detecting an incident P wave by detecting a pattern of disturbances in several discrete sensing portions of at least one optical fibre distributed acoustic sensor.

8. A method as claimed in claim 7 including the step of determining the direction of propagation of the P wave, said method comprising providing a plurality of optical fibre distributed acoustic sensors, and detecting disturbances in at least two separate optical fibre distributed acoustic sensors that relate to propagation of the same seismic wave.

9. A method as claimed in claim 7 comprising the step of estimating the time remaining before arrival of an S body wave.

10. A method as claimed in claim 7 comprising the step of generating one or more alarms when an incident P wave above a certain intensity threshold is detected.

11. A method as claimed in claim 7 further comprising detecting an incident S wave.

12. A method as claimed in claim 1 wherein the spatial size of the discrete sensing portions of the optical fibre distributed acoustic sensor is in the range of 10 m to 100 m.

13. A method as claimed in claim 1 wherein at least one optical fibre within the communications infrastructure that is used to provide an optical fibre distributed acoustic sensor comprises an optical fibre within an optical fibre bundle used for telecommunications.

14. A method as claimed in claim 1 wherein at least one optical fibre within the communications infrastructure that is used to provide an optical fibre distributed acoustic sensor comprises an optical fibre that is also used for telecommunications, and wherein optical pulses used for distributed acoustic sensing are time division multiplexed with communications traffic within the optical fibre.

15. A method as claimed in claim 13 wherein said at least one optical fibre within an optical fibre bundle is an otherwise unused optical fibre in the bundle.

16. A method, as claimed in claim 1, comprising the steps of detecting a significant seismic event, and comparing an acoustic profile obtained after the seismic event with an acoustic profile obtained before the event.

17. A method as claimed in claim 16 wherein the acoustic profile is acquired by integrating the acoustic response from the length of the fibre over a period of time.

18. A sensor network for detecting seismic events comprising a plurality of optical fibre distributed acoustic sensors, and at least one controller arranged to receive data from each of the plurality of optical fibre distributed acoustic sensors and analyse said data to detect a seismic event.

19. A sensor network as claimed in claim 18 wherein at least one of the plurality of optical fibre distributed acoustic sensors comprises an optical fibre within a communications infrastructure.