Since the beginning of the Mars InSight mission on 26 November 2018, over 500 marsquakes have been recorded. With magnitudes between 1 and 4, these are small events compared to terrestrial earthquakes. Only a few of these marsquakes could be reliably located, determining both the direction and distance from the seismometer. The recently detected, larger marsquakes are located in Cerberus Fossae, a long graben system about 1,200 km from Elysium Planitia, where InSight landed. They have an extensional mechanism consistent with the regional tectonic setting showing that the Martian crust is still undergoing active deformation.

In the InSight mission, data recorded on Mars are relayed back to Earth in regular transmissions, often multiple times a day, via the NASA Deep Space Network. They are promptly compiled and controlled for quality by the Jet-Propulsion Laboratory (JPL) in the U.S. and the National Centre for Space Studies (CNES) in France, and delivered to the Marsquake Service located at ETH Zurich in Switzerland. The Marsquake Service is responsible for the first analysis of the Mars data, with the goal of identifying marsquakes and releasing periodic marsquake catalogues – the starting point for further scientific investigations. This is a collaborative ground service operation that includes on-duty seismologists from ETH Zurich, Institut de physique du globe de Paris (IPGP), University of Bristol, and Imperial College London. At the start of the mission, the data recorded on Mars was full of surprises and difficult to decipher. After a full year of processing seismic data from Mars, the Marsquake Service is now able to fully characterise the signals within just a few hours after having been recorded on Mars. This performance is comparable to that achieved by modern seismic networks on the Earth.

Recognizing the successful performance of InSight, NASA has approved the extension of the mission for a second Martian year. Unfortunately, the red dust which characterises all the pictures of Mars is also accumulating on InSight’s solar panels, reducing the panel’s power production and raising concerns about the long-term operation of the mission.

To learn more about the NASA InSight mission visit www.insight.ethz.ch or https://mars.nasa.gov/insight/

Access the joint press release about the recent Marsquake.

M_Lhc makes the routine computation of local magnitudes in Switzerland entirely consistent with the state-of-the-art of engineering seismology research at the SED, and allows optimal use of the high-density Swiss National Seismic Network. What does this mean exactly, and how does MLhc differ from the previous local magnitude we used?

Earthquakes are commonly characterised using the local magnitude (M_L), originally introduced by Charles Richter in California in 1935. M_L is often found to be region dependent. In 1984, Urs Kradolfer, a former scientist at SED, calibrated M_L for Swiss earthquakes. His calculations were based on the recordings of the Swiss National Seismic Network, which comprised 23 stations at that time that recorded vertical ground motions only. At the turn of the century, Kradolfer’s model was later amended to take advantage of the next generation of 3-component digital broadband instruments in the upgraded Swiss National Seismic, in particular by using horizontal ground motion records (M_Lh).

In the last 20 years, the Swiss National Seismic network has grown significantly and now comprises more than 200 seismic stations, including over 100 high-quality strong-motion sensors. The SED is now routinely recording earthquakes at very close distances (15 to 20 km) to their focus in the ground (hypocenter), often with M_Lh much smaller than 2. Such close distances and small magnitudes are outside the calibration range of Kradolfer’s model. Another limitation of M_Lh is that station correction factors due to local soil conditions were not systematically used. However, this is crucial, particularly at strong-motion sites mostly installed in urban areas and often characterised by significant amplification of ground motions. When using M_Lh, seismologists had to reject station magnitudes from sites too close to the earthquake or with strong site amplifications. To cope with these drawbacks, the SED recently migrated to a revised local magnitude: "M_Lhc". The “c” stands for "corrected".

In summary, by design M_Lhc has been calibrated to provide magnitudes that are as similar as possible to M_Lh, yet with two considerable improvements that allow seismologists to use all stations collected in the network and provide more stable magnitudes, especially for small earthquakes:

• First, it is calibrated using a much larger dataset including many records from very close to the hypocentre. Therefore, M_Lhc allows us to include stations at distances closer than 20 km from the hypocenter.
• Second, the procedure to compute MLhc accounts for physics-based site amplification factors that are routinely calculated and updated by the SED, allowing us to use all stations regardless of site effects.

While for a simpler communication, the SED only uses the term "magnitude", the detailed information provided on the SED website always specify the earthquake magnitude type.

More information on the different magnitude types can be found here.