The decomposition of a total wave field recorded on a set of seismic traces
on parts corresponding to different body waves is one of the fundamental p
roblems of data processing. The central point of this problem is the correl
ation procedure for a seismic event (wave) on a set of recorded traces. In
order to implement this procedure, it is necessary to have a local lime cor
rection formula for a family of source-receiver pairs arbitrarily distribut
ed around a chosen central pair. This formula is derived in the work for a
2D seismic medium of arbitrary structure using a new homeomorphic imaging m
ethod called multifocusing. The presentation of multifocusing is divided in
to two parts: the basic ideas and concepts of the method, the time correcti
on formula and associated geometrical relationships form Part 1. The main c
haracteristic of the multifocusing approach is the consideration of the geo
metry of all possible wave fronts, which could be formed in the vicinity of
a chosen central source-receiver pair. Provided that a target wave exists
on a chosen central trace, then there is also a corresponding central ray a
nd an infinite family of surrounding wave tubes. The basic idea of the mult
ifocusing technique is based on the association of any pair of traces recor
ded in the vicinity of the central trace with certain ray tube belonging to
the family. This association can be always found. Considering this ray tub
e, the local time correction formula is obtained, assuming a spherical appr
oximation of two tube cross sections at the end points of central ray. In t
he case of a central ray with non-zero offset, the formula consists of the
following parameters: two velocities near the source and receiver locations
, two angles (departure and arrival) and two pairs of dual curvatures of tu
be cross-sections at the ray end points. The first four parameters are comm
on for all traces, the pairs of dual curvatures are, as a rule, specific fo
r the chosen pair of traces; the formula thus obtained could not be directl
y used in practice. The essential part of the first paper is devoted to the
parameterization of the family of dual curvatures. The exact formulas deri
ved for these curvatures include as parameters, a pair of dual curvatures o
f two chosen fundamental ray tubes. Different choices for the fundamental r
ay tubes are considered and important relationships between the dual curvat
ures and spreading functions for these tubes are established. They are the
generalization of the Hubral formula [Hubral, P., 1983. Computing true ampl
itude reflections in a laterally inhomogeneous earth. Geophysics 48, 1051-1
062] and known reciprocity relations. In the case of a zero-offset central
ray, most important for reflection shooting, the formulas derived are signi
ficantly simplified and involve four parameters only. The results obtained
can be used not only in the multifocusing method, but also in migration and
forward modeling. (C) 1999 Elsevier Science B.V. All rights reserved.