Quakefinder Blog

Lightning strikes are a common occurrence which QuakeFinder sites can detect. Unfortunately, a lightning strike looks very similar to the earthquake pulses that we look for prior to large quakes. The rise time of a lightning strike’s magnetic component is faster, and the lightning pulse duration is shorter than the ground-based magnetic pulses. Utilizing information provided to us by our friends at Earth Networks, we also have independent confirmation for lightning strikes. They generously donate daily lightning event files for the entire planet. We are tuning our algorithms to sort through these large files to select the strikes at an appropriate distance from each of our 140 sites to “mask out” the suspect pulses. The remaining pulses are then counted for analysis of pre-quake activity.

In addition to contaminating our data, lightning can actually damage our equipment. Our site in Hangshen, Taiwan was hit by lightning which fried all the electronics and damaged the battery. This site is being replaced this month in addition to two new sites installed in Taiwan. Earlier this month, a lightning strike destroyed a 120VAC surge suppressor feeding our site in Pt. Arena, California. Tim, the site owner at that location, identified the problem and quickly replaced the surge suppressor. Thank you Tim! We appreciate all our site owners for allowing us to use their land and assisting with minor maintenance.

The 32 Day Pulse Plot is created after the Daily Pulse Plot, and mesures the rate of daily pulses. It shows pulse counts of geomagnetic pulses that QuakeFinder has found from the selected site in a 32 day period. There are three traces, red, green, and blue that correspond to the North-South, East-West, and Vertical components of the geomagnetic signal respectively. Each trace shows the count of pulses in a 24-hour period, and there are four points in each day, meaning the 24-hour periods overlap each other by 75% and 128 counts are shown on every plot. When the geomagnetic signal trace pulse counts exceeds the count limit at any time, the QuakeFinder team is notified, triggering further analysis. These limits are constantly being refined, and may change monthly, daily, or hardly at all, depending on how the site behaves. An example from our Dang Hwa site in Taiwan is shown here: Layers of the 32 Day Pulse Plot are:

Kp Planetary Activity

Published by NOAA (The National Oceanic and Atmospheric Administration) as a global value every hour. The level of activity in the Earth’s geomagnetic field is represented by an indicator in the range of 1-3 (Green), 4-6 (Yellow) and 6-9 (Red). The highest levels of activity can generate large signals that are seen across the QuakeFinder network. The Kp indicators are spaced one hour apart and are proportionally taller for higher levels of activity. These are the same as the KP markers on the Daily Pulse Plot, only there are 32x as many on the plot.

Earthquake Markers

This is a compound Marker that is overlaid onto the geophone trace. In the example above, several m5+ plus earthquakes are shown. The magnitude is written at the top of the plot, and in this example there are two reports in the ANSS catalog, and therefore two markers are drawn here almost on top of each other. The diamond gets larger for larger quakes, but range, depths, and compass bearing are also given by the mark. Range to an earthquake is depicted by the ladder rungs rising above the diamond, in this case the quake is 44 Km from the site. Each ladder rungs denotes 10 Km. Depth is depicted by the down ladder rungs, each also 10 Km spaced. Compass bearing is shown by the lines angled down to the left, in this case the earthquake is to the Southwest of the site. Sometimes multiple quakes occur in rapid succession, and on the scale of 32 days, their markers are so close together that they overwrite each other. This is normal behavior.

Pulse Count Limits

These are the red, green, and blue horizontal lines that indicate the triggering pulse counts that will alert the QuakeFinder team.

Pulse Count Traces

These are the red, green, and blue signals that sometimes cross the Pulse Count Limits. These events are know as “Limit Excursions” and they are reported into a database and to the QuakeFinder team. Vertical ticks are added to the traces to indicate that indeed the database entries were made.