<PAGE>
 

          ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K

                1.4. THIRD AMENDMENT TO NOTE PURCHASE AGREEMENT
                   (1/19/96) DATED DECEMBER 20, 1996 BETWEEN
                      UNIVERSAL SEISMIC ASSOCIATES, INC.
                                  AND RIMCO.

<PAGE>
 
                  THIRD AMENDMENT TO NOTE PURCHASE AGREEMENT

     This Third Amendment to Note Purchase Agreement (this "First Amendment") 
dated as of December 20, 1996 is between UNIVERSAL SEISMIC ASSOCIATES, INC., a 
Delaware corporation (the "COMPANY"), and RIMCO PARTNERS, L.P., a Delaware 
limited partnership, RIMCO PARTNERS, L.P. II, a Delaware limited partnership,
RIMCO PARTNERS, L.P. III, a Delaware limited partnership, and RIMCO PARTNERS,
L.P. IV, a Delaware limited partnership (collectively, the "NOTEHOLDERS").

                            PRELIMINARY STATEMENTS

     A.  The Company and the Noteholders have heretofore entered into that 
certain Note Purchase Agreement, dated January 19, 1996, as amended by that 
certain First Amendment dated May 28, 1996 and that certain Second Amendment 
dated August 13, 1996 (as so amended, the "NOTE AGREEMENT").

     B.  The Company and the Noteholders now desire to amend the Note Agreement 
with respect to the matters set forth herein.

     C.  Capitalized terms used herein shall have the respective meanings 
described thereto in the Note Agreement unless herein defined or the context 
shall otherwise require.

                                  AGREEMENTS

     NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration the receipt and sufficiency of which is hereby
acknowledged, the Company and the Noteholders agree as follows:

SECTION 1.  AMENDMENTS.

     1.1    Section 5.16 of the Note Agreement is amended in its entirety to 
read as follows:

            "SECTION 5.16. CAPITALIZATION. The authorized capital stock
     of the Company consists solely of 20,000,000 shares of $.0001 par
     common stock, of which 5,229,109 shares are issued and outstanding."

     1.2    The following defined terms in Annex A of the Note Agreement are 
amended in their entirety to read as follows:

            "SUBSIDIARY NOTE AGREEMENT" means that certain Note Purchase
     Agreement, dated December 20, 1996, among UNEXCO and the Noteholders,
     as amended or modified from time to time.


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            "SUBSIDIARY NOTES" means the 12% Senior Secured General
     Obligation Notes, in the maximum aggregate principal amount of
     $4,000,000 issued by UNEXCO under the Subsidiary Note Agreement.

SECTION 2.  REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

     2.1    The Company represents and warrants to the Noteholders that:

            (a)  this Third Amendment has been duly authorized, executed and
     delivered by it and this Third Amendment constitutes the legal, valid and
     binding obligation of the Company enforceable against it in accordance
     with its terms, except as enforcement may be limited by bankruptcy,
     insolvency, reorganization, moratorium or similar laws or equitable
     principles relating to or limiting creditors' rights generally;

            (b)  The Note Agreement, as amended by this Third Amendment,
     constitutes the legal, valid and binding obligation of the Company
     enforceable against it in accordance with its terms, except as enforcement
     may be limited by bankruptcy, insolvency, reorganization, moratorium or
     similar laws or equitable principles relating to or limiting creditors'
     rights generally;

            (c)  the execution, delivery and performance by the Company of this
     Third Amendment (i) has been duly authorized by all requisite corporate
     action and, if required, shareholder action, (ii) does not require the
     consent or approval of any governmental or regulatory body or agency, and
     (iii) will not (A) violate (1) any provision of law, statute, rule or
     regulation or its certificate of incorporation or bylaws, (2) any order of
     any court or any rule, regulation or order of any other agency or
     government binding upon it, or (3) any provision of any material indenture,
     agreement or other instrument to which it is a party or by which its
     properties or assets are or may be bound, or (B) result in a breach or
     constitute (alone or with due notice or lapse of time or both) a default
     under any such indenture, agreement or other instrument;

            (d)  as of the date hereof and after giving effect to this Third
     Amendment, no Default or Event of Default has occurred which is continuing;
     and

            (e)  all representations and warranties in Article V of the Note
     Agreement and in the other Transaction Documents are true and correct in
     all material respects with the same force and effect as if made by the
     Company on and as of the date hereof.

SECTION 3.  CONDITIONS TO EFFECTIVENESS OF THIS THIRD AMENDMENT.

     3.1    This Third Amendment shall not become effective until, and shall 
become effective when, each of the following conditions shall have been 
satisfied:

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            (a)  executed counterparts of this Third Amendment, duly executed by
     the Company and the Noteholders, shall have been delivered to the
     Noteholders;

            (b)  the Noteholders shall have received a copy of the resolutions
     of the Board of Directors of the Company authorizing the execution,
     delivery and performance by the Company of this Third Amendment, certified
     by its Secretary or an Assistant Secretary;

            (c)  the representations and warranties of the Company set forth in
     SECTION 2 hereof are true and correct on and as of the date hereof; and

            (d)  the Noteholders shall have received the favorable opinion of
     counsel to the Company as to the matters set forth in SECTIONS 2.1(A),
     2.1(B) AND 2.1(C) hereof, which opinion shall be in form and substance
     satisfactory to the Noteholders.

SECTION 4.  PAYMENT OF NOTEHOLDERS' COUNSEL FEES AND EXPENSES.

     4.1    The Company agrees to pay upon demand, the reasonable fees and 
expenses of Andrews & Kurth L.L.P., counsel to the Noteholders, in connection 
with the negotiation, preparation, approval, execution and delivery of this 
Third Amendment.

SECTION 5.  MISCELLANEOUS.

     5.1    This Third Amendment shall be construed in connection with and as 
part of the Note Agreement, and except as modified and expressly amended by this
Third Amendment, all terms, conditions, and covenants contained in the Note 
Agreement, the Notes and the other Transaction Documents are hereby ratified and
shall be and remain in full force and effect.

     5.2    Any and all notices, requests, certificates and other instruments 
executed and delivered after the execution and delivery of this Third Amendment 
may refer to the Note Agreement without making specific reference to this Third 
Amendment but nevertheless all such references shall include this Third 
Amendment unless the context otherwise requires.

     5.3    The descriptive heading of the various Sections or parts of this 
Third Amendment are for convenience only and shall not affect the meaning or 
construction of any of the provisions hereof.

     5.4.   This Third Amendment shall be governed by and construed in 
accordance with New York law.

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                        UNIVERSAL SEISMIC ASSOCIATES, INC.


                        By: /s/ MICHAEL J. PAWELEK
                           ------------------------------------
                        Name:  Michael J. Pawelek
                        Title: President



                        RIMCO PARTNERS, L.P.,
                        RIMCO PARTNERS, L.P. II,
                        RIMCO PARTNERS, L.P. III, AND
                        RIMCO PARTNERS, L.P. IV

                        By:   RESOURCE INVESTORS MANAGEMENT COMPANY
                              LIMITED PARTNERSHIP, THEIR GENERAL PARTNER

                        By:   RIMCO ASSOCIATES, INC.,
                              ITS GENERAL PARTNER


                        By: /s/ GARY MILAVEC
                           ------------------------------------
                        Name:  Gary Milavec
                        Title: Vice President



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