# Magnitude of disturbance from a seismic source

Series | Geophysical References Series |
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Title | Problems in Exploration Seismology and their Solutions |

Author | Lloyd P. Geldart and Robert E. Sheriff |

Chapter | 2 |

Pages | 7 - 46 |

DOI | http://dx.doi.org/10.1190/1.9781560801733 |

ISBN | ISBN 9781560801153 |

Store | SEG Online Store |

## Contents

## Problem 2.3a

Firing an air gun in water creates a pressure transient a small distance away from the air gun with peak pressure of 5 atmospheres ( Pa). If the compressibility of water is /Pa, what is the peak energy density?

### Background

Air guns (see problem 7.7) suddenly inject a bubble of high‐pressure air into the water to generate a seismic wave.

Stresses acting upon a medium cause energy to be stored as strain energy, because the stresses are present while the medium is being displaced. *Strain energy density* (energy/unit volume) is equal to [see Sheriff and Geldart, 1995, equation (2.22)]

**(**)

### Solution

From problem 2.1c, we see that Pa. Also, for water, so . From equation (7,5) of Table 2.2a we find that when . Also, (see equation (2.1f)), so

Using equation (2.3a) we find that

[The dimensions of are the same as those of stress, since strains are dimensionless. Thus, stress units are .]

## Problem 2.3b

If the same wave is generated in rock with Pa, what is the peak energy density? Assume a symmetrical -wave with for .

### Solution

We have , , so equation (2.3a) becomes

Equation (9,3) in Table 2.2a gives so that

## Continue reading

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Interrelationships among elastic constants | Magnitudes of elastic constants |

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Introduction | Partitioning at an interface |

## Also in this chapter

- The basic elastic constants
- Interrelationships among elastic constants
- Magnitudes of elastic constants
- General solutions of the wave equation
- Wave equation in cylindrical and spherical coordinates
- Sum of waves of different frequencies and group velocity
- Magnitudes of seismic wave parameters
- Potential functions used to solve wave equations
- Boundary conditions at different types of interfaces
- Boundary conditions in terms of potential functions
- Disturbance produced by a point source
- Far- and near-field effects for a point source
- Rayleigh-wave relationships
- Directional geophone responses to different waves
- Tube-wave relationships
- Relation between nepers and decibels
- Attenuation calculations
- Diffraction from a half-plane