Complex sentence: This requires a careful assessment of historical data in terms of their reLKklklklded to fill the gaps in the instrumental record, particularly in areas with either relatively low seismicity or where the repeat periods for major earthquakes is more than a hundred years.
Split into simpler sentences: This requires a careful assessment of historical data in terms of their reliability. However, such data is needed to fill the gaps in the instrumental record, particularly in areas with either relatively low seismicity or where the repeat periods for major earthquakes is more than a hundred years.