WHAT’S THE DIFF?
2010 Fault Trace vs. 2015 Fault Trace vs. Current Fault Trace
If you knew where the fault line was in 2010 or 2015, chances are today it moved …farther or nearer, or you’re on it.
For the past 15 years, PHIVOLCS has used at least three types of fault traces (lines made with mapping software depicting geological faults) for the Valley Fault System. It first came to notice in 2010 as blue lines that later turned to red on Google Earth topography –which here is referred to as the 2010 FAULT TRACE, and later a change was noted with it in 2015 becoming orange and red; hence its reference here as the 2015 FAULT TRACE.
If there were other divergent and differing versions before and after these mentioned years are not known.
At close inspection, the 2015 Fault Trace generated from PHIVOLCS’ Valley Fault System Atlas deviates from the 2010 Fault Trace at most minute points. This means structures thought to be sitting atop a fault line may not be sitting there at all, and those next to or thought lucky to be spared from being on a fault line may turn out to be lying on the fault surprisingly. With the 2015 Fault Trace, it would seem that new fault lines appear while many of the old (blue) ones from 2010 disappeared. Yet the simple explanation is, plotted points shifted thus making the faults appear to move several meters away from their previous locations.
For naming convenience, PHIVOLCS’ current fault trace that this blog replicates is named CURRENT FAULT TRACE. It visibly shares similar characteristics with the 2015 Fault Trace as regards plotted points and lines in almost the same areas and directions they bend to. In fact, it can be said at a glance that both the 2015 Fault Trace and Current Fault Trace appear the same despite the latter’s thicker line, deep red color, deliberate rendering of solid line, and the green transparent matte sometimes used to distinguish it from the 2015 Fault Trace.
What is different? Though the Current Fault Trace has similar characteristics with the 2015 Fault Trace, its location is OFFSET by some 6 to 10 meters and some up to less than one meter apart; or like two athletes instead of running on the same track of a running oval, one sidesteps from the track that both are on and runs along with the other athlete on the track next beside.
How it appears for most of the 110 kilometers stretch of the Valley Fault System, the Current Fault Trace and the 2015 Fault Trace look like the parallel rails of a winding railroad track, with the repeating short supports in the middle holding the rails together their varying offset distance.
One way of understanding an explanation given by an official source is, apparently, the BASEMAP of the mapping software used to plot the points and lines of the 2015 Fault Trace is incompatible with the Google Earth basemap (or something like that).
To a lay person, maybe it can also be explained like printing a flawless document with a top of the line printer that prints perfectly. The difference that seemed discovered only later was the document was meant to be printed on A4 paper, but a ream of letter size paper was loaded on the printer tray. Thus, creating a barely discernible difference in the output; only this time the margins changed.
Whatever the official explanation can be, the 2010 and 2015 Fault Traces were accurate representations of the fault traces used by PHIVOLCS back in the day. The Current Fault Trace, which this blog replicates with meticulous and faithful accuracy, has apparently become both a minor yet critical correction of the 2015 Fault Trace, with as much as 6 to 10 meters offset (or the set distance the trace is moved to a plotted parallel location).
As inferred from PHIVOLCS’ Valley Fault System Atlas, which touched on an advanced technology called LIDAR, using laser to measure distances and strip the earth bare of surface features and identify subtle fault traces, the 2015 Fault Trace could be said was “laser accurate,” perfect even. The necessary tweaking that became the Current Fault Trace might have happened a short time after or years after the 2015 Fault Trace became public.
It does not matter when the correction was. What matters is it was corrected. And allowing the public to know about it would likewise correct an otherwise indelible wrong perception.
The Current 2025 Fault Trace is reliable given it has taken 10 years since 2015 to maintain an almost mirror image of the 2015 Fault Trace without any major changes and deviation in the plotting of points and lines. Most of all, the basemap used has been corrected and is accurate to translate correctly the fault traces, including fissures, for the Google Earth program, which is the more familiar and popular platform to the public.
The information blitz accompanying the launching of the Big One campaign a decade ago sparked a major interest in the West and East Valley Faults. People scrambled for knowledge to know if they were safe, that their homes were not in the path of a fault line. Now it may turn out some people were. And those who worried deserve a big sigh of relief if they know now they were after all unaffected.
The truth can set people free.
