How does a magnitude 3.9 earthquake compare with larger quakes?

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1. 1

   Elastic energy release in great earthquakes and eruptions

   Frontiers in Earth Science (Guðmundsson)Published May 27, 2014Checked Oct 19, 2026

   “This formula can be used as a basis for a new eruption magnitude scale, based on elastic energy released, which can be related to the moment-magnitude scale for earthquakes. For very large eruptions (>100 km3), the volume of the feeder-dike is negligible, so that the decrease in chamber volume during an eruption corresponds roughly to the associated volume of erupted materials , so that the elastic energy is . Using a typical excess pressures of 5 MPa, it is shown that the largest known eruptions on Earth, such as the explosive La Garita Caldera eruption (27-28 million years ago) and largest single (effusive) Colombia River basalt lava flows (15-16 million years ago), both of which have estimated volumes of about 5000 km3, released elastic energy of the order of 10EJ. For comparison, the seismic moment of the largest earthquake ever recorded, the M9.5 1960 Chile earthquake, is estimated at 100 ZJ and the associated elastic energy release at 10EJ.”

2. 2

   The largest induced earthquakes during the GEOVEN deep geothermal project, Strasbourg, 2018–2022: from source parameters to intensity maps

   Geophysical Journal International (Lengliné et al.)Published Apr 27, 2023Checked Oct 19, 2026

   “The third (Mlv 3.3) was initiated three weeks after shut-in on 2021 January 22, while the largest earthquake to date (Mlv 3.9) occurred on 2021 June 26, more than 6 months after shut-in. We constrained these four events’ absolute locations using a 3-D velocity model of the area and here present regional intensity maps. We estimated moment magnitude and focal mechanism trough waveform inversion and inferred the fault plane activated during the largest event from an analysis of rupture directivity effects in the recorded waveforms. Our analysis highlights the existence of a critically stressed fault that hosted three of these widely felt events. We show how the derived source properties of these four earthquakes are directly linked to ground shaking observations at the surface. Notably, we demonstrate how earthquake moment, location, direction of rupture and stress drop impact the regional intensity distribution. Our results suggest that the traffic light system could benefit from including ground shaking scenarios based on realistic subsurface properties and potential earthquake source models.”

3. 3

   A database of damaging small-to-medium magnitude earthquakes

   Journal of Seismology (Nievas et al.)Published Jan 9, 2020Checked Oct 19, 2026

   “The two main purposes were to facilitate studies on the potential for earthquakes in this magnitude range to cause material damage and to carry out a statistical study to characterise the frequency with which earthquakes of this size cause damage and/or casualties (published separately). The present paper describes the data sources and process followed for the compilation of the database, while providing critical discussions on the challenges encountered and decisions made, which are of relevance for its interpretation and use. The geographic, temporal, and magnitude distributions of the 1958 earthquakes that make up the database are presented alongside the general statistics on damage and casualties, noting that these stem from a variety of sources of differing reliability. Despite its inherent limitations, we believe it is an important contribution to the understanding of the extent of the consequences that may arise from earthquakes in the magnitude range of study.”

4. 4

   The 2002 M5 Au Sable Forks, NY, earthquake sequence: Source scaling relationships and energy budget

   Journal of Geophysical Research Atmospheres (Viegas et al.)Published Jul 1, 2010Checked Oct 19, 2026

   “We use a multitaper code that performs the complex spectral division with minimum frequency leakage and allows transformation back to the time domain to check the validity of the EGF event. We estimate source parameters for 22 earthquakes (M1–M5) in the sequence. The median stress drop of 104 MPa (using Madariaga source model, and 19 MPa for a Brune model) is significantly larger than estimates for interplate earthquakes. The lower crustal strain rates, and longer fault healing times in intraplate environments, may be responsible for this high average value. We find constant stress drop between M2 and M5, up to the bandwidth resolution limit (80 Hz) of the study, and no evidence of stress drop breakdown for M2 to M1 earthquakes. We find consistently high radiated seismic energy and apparent stress, and a median radiated energy to seismic moment ratio of 9 × 10−5. This is significantly larger than estimates for interplate earthquakes (∼2 × 10−5) and consistent with higher stress drops and stronger faults.”

5. 5

   Magnitude dependence of radiated energy spectra: Far‐field expressions of slip pulses in earthquake models

   Journal of Geophysical Research Atmospheres (Shaw)Published Feb 1, 2003Checked Oct 19, 2026

   “The other, the peak amplitude of the spectral average acceleration or the low‐frequency corner in the case of a flat acceleration spectrum, occurs at a period that scales with the duration of slip of points on the fault. The period of the peak spectral acceleration saturates for large events. Looking at the rupture motions on the fault, we find that this spectral behavior corresponds with the behavior of slip pulses in the model. Intense narrow pulses of slip develop for very long rupture events. We quantify this by measuring the mean slip duration as a function of rupture length and show that it is has the same behavior as the peak period of spectral acceleration. Thus the duration of the slip pulses in these ruptures is directly expressed in their radiated spectra. Moreover, we find that these corner periods exhibit a nontrivial dependence on event magnitude for the different frictional instabilities that we have examined, suggesting that any observed dependence of these corner periods on earthquake magnitude might provide insight into the frictional instability of earthquakes.”