Describe how SISTEM detects, associates and sizes earthquakes

docs/events/how-detection-works.md

@@ -9,16 +9,32 @@ SISTEM receives seismic waveforms from your sensors, picks candidate arrivals at
 ```text
 Sensor waveforms
       ↓
-Candidate station detections
+Pick: each channel is watched for a sudden rise in energy
       ↓
-Association across stations
+Associate: P-wave picks from several stations are grouped into one earthquake
       ↓
-Estimated origin, location, depth, and magnitude
+Locate and size: origin time, latitude, longitude, depth, and magnitude
       ↓
-Event catalog and notifications
+Event catalog, live map, and notifications
 ```
 
-## Why multiple stations matter
+## The steps
+
+**Picking.** SISTEM compares each channel's short-term average energy with its long-term average (STA/LTA). When the short-term level jumps above the background, it records a **pick**: the time a seismic wave arrived at that station. Picks on different channels of the same station within 3 seconds count as one station.
+
+**Association.** SISTEM groups P-wave picks from different stations that fit a single earthquake, using the GaMMA association method and a P-wave speed of 6 km/s. It works with P waves only.
+
+- A **candidate** event needs P-wave picks from at least **3 stations**.
+- An event is **published**, to the catalog, the live map, and notifications, once at least **4 stations** have picked it.
+- Only stations that are online are taken into account.
+
+**Location.** The event is located within the monitoring region Grillo sets for your network, at a depth of up to 100 km.
+
+**Magnitude.** Magnitude is estimated from the size of the first P-wave motion at each station (its peak displacement) and the station's distance from the event. This kind of magnitude is available quickly, which suits early warning, but it is an early estimate.
+
+**Updates.** An event can be refined as more stations report. Its values settle about a minute after the last new pick.
+
+## Why several stations are needed
 
 One station can record motion but normally cannot determine a unique earthquake location. Association compares arrival times across geographically separated stations. Network geometry, station timing, noise, outages, and distance from the source all affect the result.
 
@@ -41,4 +57,4 @@ Electronic communication is faster than damaging seismic waves, but detection an
 
 ## Deployment-specific configuration
 
-Detection thresholds, association configuration, velocity models, alert policies, and external integrations are managed for each deployment. Grillo configures them for your project; they are not settings you can change in Grillo Cloud.
+Grillo configures detection for your network: the monitoring region, detection thresholds, association settings, and the velocity model. If a sensor channel is damaged or too noisy, Grillo can exclude it from detection while still recording it. These are not settings you can change in Grillo Cloud; [contact Grillo Support](/support/contact) to ask for a change.

docs/events/index.md

@@ -10,7 +10,7 @@ SISTEM gives you:
 
 - **Waveforms.** Watch each sensor's live waveform and spectrogram, review recorded data, and [download it as CSV](/dashboard/data/waveforms).
 - **An automatic event catalog.** Each detected earthquake is recorded with its time, location, depth, and magnitude.
-- **A live map.** Watch detections as they happen, with the stations that triggered and the estimated wave fronts.
+- **A live map.** Watch detections as they happen, with the stations that triggered and the estimated wave fronts, or run a simulation.
 - **In-app alerts.** Grillo Cloud shows a notification and an unread count on **Events** when a new earthquake is detected.
 
 Events and the live map appear in the **Seismic** group of the sidebar. Waveforms appear in each sensor's details.
@@ -19,7 +19,7 @@ Events and the live map appear in the **Seismic** group of the sidebar. Waveform
 
 - SISTEM enabled for your project. [Contact Grillo](/support/contact) to add it.
 - Sensors sending seismic data to Grillo. Detection does not run on data that goes to [your own server](/dashboard/data/data-server).
-- Enough stations, spread around the area you want to monitor. An earthquake is located from several stations' arrivals. See [How Detection Works](/events/how-detection-works).
+- Enough stations, spread around the area you want to monitor. An event is only published once at least four stations have detected it. See [How Detection Works](/events/how-detection-works).
 
 ## Guides
 

docs/events/live-map.md

@@ -22,7 +22,9 @@ The **Legend** explains each symbol.
 
 ## Live mode
 
-When stations start detecting shaking, the **Event Log** lists each station pick as it arrives. Once enough stations have picked, SISTEM locates the event and the map shows its magnitude, epicenter, and the cities the waves will reach.
+The **Live** button shows whether the map is connected to SISTEM: **Connected**, **Connecting**, or **Disconnected**. If it stays disconnected, refresh the page.
+
+When stations start detecting shaking, each pick plays a short beep and the **Event Log** lists the pick. Once at least four stations have picked, SISTEM locates the event and the map shows its magnitude, epicenter, and the cities the waves will reach.
 
 ## Map settings