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Sunday
Oct302016

30 October Central Italy (Norcia) Earthquake (M6.6)

A strong earthquake struck the mountainous Appenine region of central Italy this morning, part of a prolonged sequences of earthquakes that began in August and included several significant events. The map below shows large events from the last 30 days (data from the USGS).

The channels below correspond to the closest real-time seismic station (operated by MedNet), which is located in L'Aquila, about 50 km to the southeast. You should be able to monitor larger aftershock activity by watching that station.  

SIGNALPARAMETERS; 2016-10-30 06:40:09; 60;  10; 0.5; -4.0 
MN; AQU; --; BHZ; L'AQUILA, ITALY - UP-DOWN
MN; AQU; --; BHE; L'AQUILA, ITALY - EAST-WEST
MN; AQU; --; BHN; L'AQUILA, ITALY - NORTH-SOUTH

The image below shows the main shock signals (red dashed line is the origin time), followed by numerous aftershock signals.

The map below shows 3853 epicenter locations obtained from the Istituto Nazionale di Geofisica e Vulcanologia (INGV) of Italy. The map includes earthquakes with M ≥ 2.0. Symbol areas are scaled logartihmically to show a representative size of the earthquakes. The maps includes earthquakes that occurred between August and this morning.

Each earthquake's symbol area is sized roughly to correspond with a "typical" rupture area of an earthquake of the corresponding magnitude. I used a simple forumula, but the area is generally within a factor of two of the actual area. Of course, large earthquake ruptures are not often circular in shape and the rupture may not be cetered on the epicenter.

Below is a projection of the earthquakes (from the INGV) from August through the present onto a plane strike 142N and dipping 42° to the southwest (the faults involved in this sequence are not well modeled by a single plane).

The lateral origin is the largest earthquake in August, events to the left are to the north and depth increases from top to bottom. The symbol sizes are scaled as in the map above - to crudely approximate the relative areas of the ruptures. The circles are centered on the hypocenter, but they may not have ruptures with that configuration.

The chart below is an Omori's Law diagram for the sequence thus far. The last day is only partly over - so the last bar will increase in height.

Below is a Gutenberg-Richter Diagram for the August-October activity. The corresponding "b" value is roughly 0.82. 

Again, these data are credited to Italy's INGV (http://www.ingv.it/en/) - they are doing a superb job sharing the data and results.