What is the difference between an earthquake's magnitude and intensity?

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1. 1

   Seismic magnitude scales (Wikipedia)

   WikipediaPublished Oct 15, 2026Checked Oct 17, 2026

   “Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary based on what aspect of the seismic waves are measured and how they are measured. Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.”

2. 2

   Moment magnitude scale (Wikipedia)

   WikipediaPublished Oct 16, 2026Checked Oct 17, 2026

   “The moment magnitude scale (MMS; denoted explicitly with Mw or Mwg and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. Mw was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Before Hanks and Kanamori (1979) , Kanamori (1977) developed Mw scale for large earthquakes above 7.5. Thus Mw and M are not the same mathematically even though they are considered the same. Similar to the local magnitude/Richter scale (ML) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale. Moment magnitude (Mw) is considered the authoritative magnitude scale for ranking earthquakes by size. It is more directly related to the energy of an earthquake than other scales, and does not saturate – that is, it does not underestimate magnitudes as other scales do in certain conditions.”

3. 3

   The high-frequency magnitude (m3Hz) of Italian earthquakes from intensity data - the ICEM Catalog.

   Scientific data (Parolai et al.)Published Jun 6, 2026Checked Oct 17, 2026

   “The assessment of seismic hazard and risk requires a catalogue of earthquakes (both historical and recorded during the instrumental era), where the location and magnitude of events affecting the study area are reported. Mw is commonly used for this aim, but it is a static measure of earthquake size and it cannot capture the full extent of earthquake source complexity. Other magnitude scales connected to the rupture kinematics and dynamics should complement Mw in hazard studies, but this required efforts in re-analyzing catalogs of intensity data. To this aim, we developed a high-frequency magnitude (m3Hz) estimated using a random or log-averaged horizontal component of ground motion from frequencies above the highest corner frequency of the earthquake source spectrum. Here, we apply the novel procedure to the intensity data from the Parametric Catalogue of Italian Earthquakes (CPTI15). We derive m3Hz for 1,951 earthquakes (from 1117 to 2020). The new earthquake catalog is defined by the acronym ICEM. For all earthquakes a quality index based on the variance-to-mean ratio (VMR) has been assigned.”

4. 4

   Insights into the seismogenesis and tectonic implications of an isolated intraplate earthquake (M4.0) on February 17, 2025, in Delhi.

   Scientific reports (Prajapati et al.)Published Jan 30, 2026Checked Oct 17, 2026

   “Data from the dense network of the National Seismological Network (NSN) enabled precise focal mechanism determination, indicating predominantly strike-slip faulting at a centroid depth of 41 km. Fault-plane solutions and strong-motion recordings suggest rupture along a NW-SE-oriented fault system, associated with the pre-existing Sohna and Mathura Faults. The maximum peak ground acceleration (PGA) recorded at the nearest station (~ 25 km) was 0.0026 g. No aftershocks were observed in the six months following the mainshock, suggesting a stable post-seismic regime. Stress field inversion aligns with the regional strike-slip stress environment, consistent with the seismicity pattern since 1960. Local subsurface heterogeneities including weak rock zones, fluid-saturated sediments, and relict riverine deposits likely influenced the rupture initiation. The earthquake is interpreted as a strike-slip event triggered by fluid-assisted weakening (hydrofracturing) of fault zones. These findings underline the role of crustal fluids in Delhi's intraplate seismicity and provide valuable constraints on fault behaviour and earthquake hazard in the region.”

5. 5

   Occurrence of major earthquakes is as stochastic as smaller ones.

   Science advances (Ghazoui et al.)Published Feb 11, 2026Checked Oct 17, 2026

   “Seismic hazard estimates rely on interevent time distributions between earthquakes of a given magnitude. In the Himalaya, recurrence intervals are usually modeled as cyclic or quasiperiodic, whereas globally, they range from periodic and clustered to random. Statistical analyses of a 6000-year lake-sediment seismic record, calibrated against regional instrumental data, worldwide paleoseismic records, and synthetic seismic catalogs, demonstrate that time intervals between large earthquakes (M ≥ 6.5, based on shaking intensity thresholds calibrated locally) robustly follow a Poisson distribution. Second-order fluctuations indicate event clustering. These observations contradict periodic or quasiperiodic recurrence models. Comparisons with paleoseismic data from other tectonic settings and realistic synthetic catalogs confirm the robustness and broad applicability of these findings. Thus, major earthquakes appear as stochastic as smaller ones, challenging recurrence models derived from limited datasets and substantially increasing seismic hazard estimates.”