- echelon faults on recent surfaces. Erosional features are sometimes associated with active faults but are not necessarily indi- cators of active faults. (ii) Seismolo@‘cal criteria - Earthquakes and micro-earthquakes when fairly precisely located with the aid of instruments may indicate an active fault. However, a lack of known earth- quakes should not be regarded as an indication that a fault is inactive. (iii) Historical criteria - Historical sources such as manuscripts, personal information and local traditions may contain valuable data on past earthquakes. Fault movements ox creep may be detected from displaced man-made lineaments. 6.2 Hazards during earthquakes While an earthquake is in progress, major hazards may arise as a result of the particular geological materials present in the localities where seismic shocks are taking place, Some notes on this important aspect are given in the following sub-sections, 6.2.1 Fractured bedrock on steep slopes Large masses of fractured rock forming the walls of valleys may be dislodged by a strong seismic shock. If the difference in elevation between the potentially unstable mass and the valley floor is sufficient for the mass to gain high momentum, the mode of movement will change from sliding and tumbling to an extremely rapid and destructive flow of rock fragments. 17 -- Once mobilized, such a flow has high kinetic energy and may travel a considerable distance up the opposite valley side or turn down the valley at speeds up to 200 km/h for a long distance, destroying everything in its path. An example of a very destructive rock fsll - debris avalanche - is that caused by the 31 May 1970 earthquake in Peru which caused a portion of the north-west face of Huascarsn Peak to fail. The mass crashed down on the lower slopes, picked up water and flowed with high velocity 
**Analysis**
The text primarily discusses the geological aspects of earthquakes and their potential hazards, focusing on the movement of rock fragments and the resulting destructive flows. While it does not explicitly mention economic development or any of the other categories, the discussion of hazards and destruction suggests a connection to the Natural Resources and Environment category.

**Category**
Natural Resources and Environment