We report a novel long range distributed fiber optic vibration sensor using two counter-propagating interferometers, which are space-division multiplexed in different cores of a seven-core fiber. The proposed system requires only one laser source. Thanks to the spatially separated structure of the two interferometers, it no longer suffers from the coherent Rayleigh backscattering noise, and, since forward transmitting CW light instead of weak backscattering light is used, as a result, the sensing range can be significantly extended. On the other hand, because the two interferometers are implemented in one single compact multicore fiber, the output temporal waveforms have good correlation; therefore, the sampled waveforms can be used directly to determine the vibration location through cross correlation, and no additional complicated data processing (e.g., time-frequency analysis methods) is required. For proof of concept, we achieved distributed vibration detection with 38.5 km sensing range, and the root mean square error of positioning is estimated to be about 54.9 m with 120 measurements. The proposed system has the unique advantages of simple setup, high sensitivity, large dynamic range, ultra-long sensing range, etc.