def merge_m(rec1, rec2):
    """
    Merge M records.

    Parameters
    ----------
    rec1 : sdt.seisan_M
        Seisan M record.
    rec2 : sdt.seisan_M
        Seisan M record.

    Returns
    -------
    rec1 : sdt.seisan_M
        Seisan M record.

    """
    rec1.mrr_mzz = rec2.mrr_mzz
    rec1.mtt_mxx = rec2.mtt_mxx
    rec1.mpp_myy = rec2.mpp_myy
    rec1.mrt_mzx = rec2.mrt_mzx
    rec1.mrp_mzy = rec2.mrp_mzy
    rec1.mtp_mxy = rec2.mtp_mxy
    rec1.reporting_agency2 = rec2.reporting_agency2
    rec1.mt_coordinate_system = rec2.mt_coordinate_system
    rec1.exponential = rec2.exponential
    rec1.scalar_moment = rec2.scalar_moment
    rec1.method_used_2 = rec2.method_used_2
    rec1.quality_2 = rec2.quality_2
    return rec1
