The first number people often notice in an earthquake report is magnitude. But magnitude is logarithmic rather than a simple linear scale, and the same earthquake can produce different levels of shaking in different places. This guide explains magnitude versus intensity, epicenter versus hypocenter, and how to read the map and list in sanCheck.
| Term | What it means | How to read it |
|---|---|---|
| Magnitude | A logarithmic measure of the earthquake's overall size and released energy. | Treat it as a value describing the earthquake itself. The “Magnitude” shown in sanCheck is this value. |
| Intensity | The strength of shaking experienced at a specific location. | It can vary from place to place depending on distance, ground conditions, buildings, and other factors. |
Magnitude alone cannot tell you exactly how strongly a particular neighborhood will shake.
Magnitude is logarithmic. Each increase of 1.0 corresponds to about 10 times the recorded wave amplitude and roughly 32 times the released energy. A magnitude 9 is therefore not merely “one point bigger” than a magnitude 8.
It may be felt nearby but is generally a small earthquake. Whether people feel it depends on depth, distance, and local conditions.
Shaking can be clearly noticeable. If the source is shallow or nearby, objects may fall and vulnerable structures can suffer localized damage.
A very large earthquake. A shallow event near a populated area can cause severe damage across a broad region.
These are exceptionally large earthquakes globally. They can rupture very large fault areas, and offshore events require close attention to tsunami risk.
It is among the largest earthquakes observed on Earth. In terms of energy, magnitude 9 releases roughly 32 times as much as magnitude 8, about 1,000 times as much as magnitude 7, and about 32,000 times as much as magnitude 6. Actual damage still depends heavily on depth, distance from land, local geology, building resilience, and whether a tsunami is generated.
These are approximate comparisons for understanding the scale. Magnitude alone cannot predict damage or the intensity at a particular location.
The point below the Earth's surface where the earthquake starts. When depth is reported, it helps describe how far below the surface the source was.
The point on the Earth's surface directly above the hypocenter. This is the surface location commonly used when an earthquake is plotted on a map.
The card displays earthquakes within the most recent 24-hour window. New events are reflected in the map and list in time order as data updates.
Domestic events are shown by default. When international events are available, you can include them with the “Include international” option. If there are no domestic events but international events exist, international data may be shown automatically.
Domestic events use red markers and international events use gray markers. Marker size grows with magnitude as a visual aid; it does not represent the actual damage area.
When current location is active, your position is shown on the map. Selecting an earthquake moves the map to that event, and any available detail text is shown below the list.
Safety actions vary by location and situation. During a real emergency, follow the latest official alerts and evacuation instructions.