Review of the seismicity on Mars

<p>The InSight mission collected an astounding seismic dataset from Mars during more than four years (1450 sols) of operation until it was retired on 21 December 2022.</p><p>The Marsquake Service MQS detected more than 1300 events of seismic origins. Two of these events (S1000a and S1094b) were later confirmed as distant impacts (Figure 1), with magnitudes of M_W^Ma=4.0 and 4.2 and crater diameters of 130 and 150 m, respectively. Finally, the largest marsquake (S1222a, M_W^Ma=4.6) that occurred during InSight's lifetime was recorded on May 4, 2022.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.e62564543cb368458723761/sdaolpUECMynit/32UGE&app=m&a=0&c=cd16eb97f9fcb454b579eef3a0ef4b08&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Here, we present the current understanding of the Martian seismicity and the different types of events we observed on Mars, based on the data collected over the whole mission.</p><p><strong>Low-frequency (LF) and broadband (BB)</strong><br>The LF family of events include energy predominantly below 1 Hz. They are similar to teleseismic events observed on Earth, and clear P and S waves are often identified. The hypocenter is known for about half of the recorded LF-BB events, owing to the difficulty of determining back-azimuth and in some cases also distance for the smaller events. The following elements are now understood:</p><ul><li>Seismicity appears to be located only in few spots around Mars (Figure 2) and no tectonic events were located within 25&#176; from the InSight station.</li> <li>A large number of LF-BB events are located 26&#8211;30&#176; from the station, interpreted to be associated with the active dynamics of the volcanic Cerberus Fossae area.</li> <li>A group of events show only a weak S-wave energy and are aligned using the P-wave and length of its coda to around 46&#176;. Their tectonic origin is yet unknown.</li> <li>A few events are located around 60&#176; with relatively emergent P- and S-wave energy.</li> <li>Two large events (S0976a and S1000a) lie beyond the core shadow and have PP and SS phases; S0976a in the Valles Marineris region 146&#176; away from InSight, and S1000a as the result of a meteoritic impact.</li> <li>A number of events of uncertain location are clustered in the same distance, around 100-120&#176; distance.</li> <li>LF events have the largest magnitudes with S1222a reaching M_W^Ma=4.6 and a few others at or above M_W^Ma=3.5.</li> </ul><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.75b8a4643cb364658723761/sdaolpUECMynit/32UGE&app=m&a=0&c=215bbcd60d010b3ad402775c0a49a483&ct=x&pn=gepj.elif&d=1" alt=""></p><p><strong>High-frequency (HF) </strong><br>The HF family of events are predominantly at and above the 2.4 Hz, local subsurface resonance. The HF events have magnitudes below M_W^Ma 2.5 and originate from a distance range of 25&#8211;30&#176;, likely a single area in the central Cerberus Fossae region, as very shallow events associated to active volcanic dykes.&#160;</p><p><strong>Very high frequency (VF):</strong><br>A small number of HF events are characterized by higher frequency content, up to 20&#8211;30 Hz with a notable amplification on the horizontal components at very high frequency, and are termed VF events. The amplification is plausibly explained by the local subsurface structure. These events are observed only close to the lander. Remote imaging of recent craters and the presence of a distinctive acoustic signal confirmed that the closest events were produced by meteoric impacts. Investigations are being conducted to understand if other VF events can be confirmed as impacts, too.</p>