A Method for Quantitative Assessing the Migration-Distance of Active Faults on Both Sides of Mid-Ocean Ridges——Based on Multi-Beam Bathymetry Data

The fracture-fissure systems near mid-ocean ridges are dominating conduits for the circulation of metallogenic fluid, therefore, the distribution area of active faults on both sides of mid-ocean ridges is more suitable for seafloor hydrothermal activities. Through Fourier filtering to Multi-beam bathymetry data and combining the topographic slope, curvature and slope aspect patterns, we can identify and quantitatively measure such elements of faults as Fault Spacing and Fault Heave. According to Sequential Faulting Model at Mid-Ocean Ridges, Fault Spacing and Fault Heave can be used to calculate the maximal migration-distance of an active fault on either side of the mid-ocean ridge. Choosing Mid-Atlantic Ridge 20°-24°N (NMAR) and North Chile Ridge (NCR) as two testing sites, it can be learnt that the average migration-distance of active faults is 0.76-1.01km at NMAR, which is larger at the center than the ends of this ridge segment. Moreover, the average migration-distance of active faults is 0.38-1.6km at NCR, and there are various distribution patterns for different segments. Among all studied segments of NCR, the distribution patterns of average migration-distance of active faults in N9N and N10 segments are both smaller at the center than the ends, which are opposite to the N1 and N9S segments, and the calculated results increasing from one end to the other at N5 and S5 segments, while for the N8 segment, the distribution of average migration-distance of active faults shows a `zigzag' pattern along axis. Under the condition that the number of faults for a profile with a definite length is certain, the distribution range of active faults is proportional to M values along mid-ocean ridges. However, the number of faults is affected by lithospheric thickness, M, and magmatic cycle and so on. The two testing sites can be divided into two endmembers: NMAR site is characterized by a relatively low M value, and the fault number there is mainly affected by the axial variations of M values, which result in that a higher range of faulting roughly corresponds to a low M value; while at NCR site with high M values (0.90 0.95), the fault number there is mainly influenced by the thickness of lithosphere and its axial variations, thus the range of faulting is positively related to the M values.