MODELING TIP ZONES TO PREDICT THE THROW AND LENGTH CHARACTERISTICS OFFAULTS

A map of faults in a 60 km(2) area of the southern North Sea has been produced from three-dimensional seismic data. The faults shown on the map obey power-law cumulative-frequency distributions for throw (power -law exponent, D, approximate to 2.7) and length (D approximate to 1.1 ). Simulations have been carried out to correct for sampling biases in the data and to make predictions of the throw and length scaling char acteristics of the faults. The most important bias is caused by poor r esolution;of the small displacement tip zones of faults. The raw data show considerable scatter in their length:throw ratios, but they more closely fit a linear relationship if a length of 500 m is added to eac h fault, thereby making up for the zones near the fault tips with thro ws (approximate to 15 m) below seismic resolution. Further variability in the data may be caused by such geological factors as fault interac tion. Tip lengths have been extended to simulate the actual fault patt ern in the study area. Maps produced by this procedure can be used to estimate the true connectivity of the fault network. Extending the fau lts results in greater connectivity than shown by the raw data, which may cause greater compartmentalization of the rock mass. This greater compartmentalization has implications for hydrocarbon exploitation if the faults are sealing. A problem with the model, however, is that it does not deal effectively with the interaction of subparallel, noncopl anar faults. To test the reliability of the procedure, we analyzed exp osure-scale faults in Somerset, United Kingdom, where the tips are wel l constrained. Both length-throw relationships and map-pattern connect ivity for the simulated fault networks agree closely with the actual d ata.