The Marsquake catalogue from InSight, sols 0–478 Clinton, John F.; Ceylan, Savas; van Driel, Martin ...
Physics of the earth and planetary interiors,
January 2021, 2021-01-00, 2021-01, Letnik:
310
Journal Article
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The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission began collecting high quality seismic data on Mars in February 2019. This manuscript documents the ...seismicity observed by SEIS, InSight's seismometer, from this time until the end of March 2020. Within the InSight project, the Marsquake Service (MQS) is responsible for prompt review of all seismic data collected by InSight, detection of events that are likely to be of seismic origin, and curation and release of seismic catalogues. In the first year of data collection, MQS have identified 465 seismic events that we interpret to be from regional and teleseismic marsquakes. Seismic events are grouped into 2 different event families: the low frequency family is dominated by energy at long period below 1 s, and the high frequency family primarily include energy at and above 2.4 Hz. Event magnitudes, from Mars-specific scales, range from 1.3 to 3.7. A third class of events with very short duration but high frequency bursts have been observed 712 times. These are likely associated with a local source driven by thermal stresses. This paper describes the data collected so far in the mission and the procedures under which MQS operates; summarises the content of the current MQS seismic catalogue; and presents the key features of the events we have observed so far, using the largest events as examples.
•The Marsquake Service is providing updated catalogues of Martian seismicity as recorded on InSight.•465 distant marsquakes have been identified in the first 478 martian days (sol) since InSight landed.•This version of the catalogue includes an additional 712 events that may be due to local cracking from thermal forcing.
The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed on the surface of Mars on November 26, 2018. One of the scientific instruments in the ...payload that is essential to the mission is the SEIS package (Seismic Experiment for Interior Structure) which includes a very broadband and a short period seismometer. More than one year since the landing, SEIS continues to be fully operational and has been collecting an exceptional data set which contains not only the signals of seismic origins, but also noise and artifacts induced by the martian environment, the hardware on the ground that includes the seismic sensors, and the programmed operational activities of the lander. Many of these non-seismic signals will be unfamiliar to the scientific community. In addition, many of these signals have signatures that may resemble seismic events either or both in time and frequency domains. Here, we report our observations of common non-seismic signals as seen during the first 478 sols of the SEIS data, i.e. from landing until the end of March 2020. This manuscript is intended to provide a guide to scientists who use the data recorded on SEIS, detailing the general attributes of the most commonly observed non-seismic features. It will help to clarify the characteristics of the seismic dataset for future research, and to avoid misinterpretations when searching for marsquakes.
•This paper is a summary of the InSight data from Mars, mainly focusing on the seismic data set.•We describe the signals of non-seismic origins that potentially can cause misinterpretations as marsquakes.•We outline the common features in the data such as artifacts and patterns for future reference that may be unfamiliar to the scientific community.
The instrument package SEIS (Seismic Experiment for Internal Structure) with the three very broadband and three short‐period seismic sensors is installed on the surface on Mars as part of NASA's ...InSight Discovery mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. One ubiquitous artifact in the raw data is an abundance of transient one‐sided pulses often accompanied by high‐frequency spikes. These pulses, which we term “glitches”, can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to SEIS‐internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of either the instrument or the ground. In this study, we focus on the analysis of the glitch+spike phenomenon and present how these signals can be automatically detected and removed from SEIS's raw data. As glitches affect many standard seismological analysis methods such as receiver functions, spectral decomposition and source inversions, we anticipate that studies of the Martian seismicity as well as studies of Mars' internal structure should benefit from deglitched seismic data.
Plain Language Summary
The instrument package SEIS (Seismic Experiment for Internal Structure) with two fully equipped seismometers is installed on the surface of Mars as part of NASA's InSight Discovery mission. When compared to terrestrial installations, SEIS is more exposed to wind and daily temperature changes that leads to inevitable degradation of the quality of the recorded data. One consequence is the occurrence of a specific type of transient noise that we term “glitch”. Glitches show up in the recorded data as one‐sided pulses and have strong implications for the typical seismic data analysis. Glitches can be understood as step‐like changes in the acceleration sensed by the seismometers. We attribute them primarily to SEIS‐internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the whole SEIS instrument. In this study, we focus on the detection and removal of glitches and anticipate that studies of the Martian seismicity as well as studies of Mars's internal structure should benefit from deglitched seismic data.
Key Points
Glitches due to steps in acceleration significantly complicate seismic records on Mars
Glitches are mostly due to relaxations of thermal stresses and instrument tilt
We provide a toolbox to automatically detect and remove glitches
First Focal Mechanisms of Marsquakes Brinkman, Nienke; Stähler, Simon C.; Giardini, Domenico ...
Journal of geophysical research. Planets,
April 2021, Letnik:
126, Številka:
4
Journal Article
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Since February 2019, NASA's InSight lander is recording seismic signals on the planet Mars, which, for the first time, allows to observe ongoing tectonic processes with geophysical methods. A number ...of Marsquakes have been located in the Cerberus Fossae graben system in Elysium Planitia and further west, in the Orcus Patera depression. We present a first study of the focal mechanisms of three well‐recorded events (S0173a, S0183a, S0235b) to determine the processes dominating in the source region. We infer for all three events a predominantly extensional setting. Our method is adapted to the case of a single, multicomponent receiver and based on fitting waveforms of P and S waves against synthetic seismograms computed for the initial crustal velocity model derived by the InSight team. We explore the uncertainty due to the single‐station limitation and find that even data recorded by one station constrains the mechanisms (reasonably) well. For the events in the Cerberus Fossae region (S0173a, S0235b) normal faulting with a relatively steep dipping fault plane is inferred, suggesting an extensional regime mainly oriented E‐W to NE‐SW. The fault regime in the Orcus Patera region is not determined uniquely because only the P wave can be used for the source inversion. However, we find that the P and weak S waves of the S0183a event show similar polarities to the event S0173, which indicates similar fault regimes.
Plain Language Summary
As time passes, the mysterious interior of Mars is slowly being unraveled due to the detection and analysis of Marsquakes recorded with a seismograph carried by the InSight lander. Close to 400 Marsquakes have so far been identified, yet only a handful of those show similarities to earthquakes. Those earth‐like events are located near the Cerberus Fossae and Orcus Patera regions. We take advantage of the similarity between Marsquakes and earthquakes and apply a methodology developed for earthquake characterization before seismic recorders became abundant on Earth. We find that the Marsquakes in these source regions are dominated by extensional rather than compressing features. This is important information to further understand what causes Marsquakes.
Key Points
We infer the tectonic setting in Cerberus Fossae on Mars by seismic source inversion
We present a robust inversion strategy for single‐station moment tensor inversion
Three Marsquakes recorded by InSight reveal a predominantly normal faulting regime
Given that clay‐rich landslides may become mobilized, leading to rapid mass movements (earthflows and debris flows), they pose critical problems in risk management worldwide. The most widely proposed ...mechanism leading to such flow‐like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid‐to‐liquid transition results in a dramatic reduction of mechanical rigidity in the liquefied zones, which could be detected by monitoring shear wave velocity variations. With this purpose in mind, the ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide‐earthflow was equipped with continuously recording seismic sensors during spring and summer 2010. An earthslide of a few thousand cubic meters was triggered in mid‐August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.
Key Points
Rigidity drop observed from ambient seismic noise correlation monitoring
Rigidity drop several days before the slope failure
Frequency analysis demonstrates the change to be at a depth of 9 to 11 m
The seismometer deployed on the surface of Mars as part of the InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) has recorded several hundreds of ...marsquakes in the first 478 sols after landing. The majority of these are classified as high‐frequency (HF) events in the frequency range from approximately 1 to 10 Hz on Mars' surface. All the HF events excite a resonance around 2.4 Hz and show two distinct but broad arrivals of seismic energy that are separated by up to 450 s. Based on the frequency content and vertical‐to‐horizontal energy ratio, the HF event family has been subdivided into three event types, two of which we show to be identical and only appear separated due to the signal‐to‐noise ratio. We show here that the envelope shape of the HF events is explained by guided Pg and Sg phases in the Martian crust using simple layered models with scattering. Furthermore, the relative travel times between these two arrivals can be related to the epicentral distance, which shows distinct clustering. The rate at which HF events are observed varies by an order of magnitude over the course of one year and cannot be explained by changes of the background noise only. The HF content and the absence of additional seismic phases constrain crustal attenuation and layering, and the coda shape constrains the diffusivity in the uppermost shallow layers of Mars.
Plain Language Summary
The high‐frequency events are the most commonly observed class of marsquakes by the InSight mission. As the frequency content and signal shape over time is different from seismic events (i.e., events that excite elastic waves traveling in the subsurface such as earthquakes, impacts, or explosions) observed both on Earth and the Moon, these were not immediately recognized as signals of seismic origin. This paper shows that these signals can be explained by distant shallow small quakes together with wave propagation effects in the Martian crust. This interpretation opens the possibility to use these signals to probe the material properties of the crust and raises the question which physical process causes these events.
Key Points
InSight’s seismometers have recorded several hundreds of events at frequencies between 1 and 10 Hz
The envelopes of these events can be explained by seismic waves guided in the crust over significant distances
This observation helps to constrain the elastic properties of the shallow structure
Mars atmospheric pressure variations induce ground displacements through elastic deformations. The various sensors of the InSight mission were designed in order to be able to understand and correct ...for these ground deformations induced by atmospheric effects. Particular efforts were made, on one hand, to avoid direct pressure and wind effects on the seismometer and, on the other hand, to have a high performance pressure sensor operating in the same frequency range as the seismometer. As a consequence of these technical achievements and the low background seismic noise of Mars, the InSight mission is opening a new science domain in which the ground displacements can be used to perform atmospheric science. This study presents an analysis of pressure and seismic signals and the relations between them. After a short description of the pressure and seismic sensors, we present an analysis of these signals as a function of local time at the InSight location. Then the coherent signals recorded by both pressure and seismic sensors are described and interpreted in terms of atmospheric signals and ground deformation processes. Two different methods to remove the pressure effects recorded by SEIS sensors are presented, and their efficiency is estimated and compared. These decorrelation methods allow the pressure generated noise to be reduced by a factor of 2 during the active day time period. Finally, an analysis of SEIS signals induced by gravity waves demonstrates the interest of ground displacement measurements to characterize their arrival azimuth.
Key Points
Coherence between pressure and seismic measurements is high in the 0.05–0.3 Hz range during active day time periods
Atmospheric noise can be removed efficiently from seismic records in the frequency ranges where coherence is high
Arrival azimuth of night time atmospheric gravity waves is estimated from SEIS data
We present a new class of seismic signals that are recorded by the seismometer placed on the surface of Mars as part of the NASA InSight mission. The signals, termed super high frequency (SF) events, ...are of short duration (∼20 s), are often similar in amplitude, and feature high‐frequency energy between ∼5 and 30 Hz that is dominant on the horizontal components. For detection and characterization of SF events, we employ the available continuous 20 samples per second (sps) data from the Very Broadband instrument. Due to bandwidth limitations, 100 sps data from the short‐period sensor are only partially obtainable, but they aid in analysis of the frequency content above 10 Hz and in distinguishing the events from high‐frequency noise. From June 2019 to May 2020, 780 SF events have been detected. The events observed occur in repeatable patterns that last for weeks. Initially, the SF events were clustered in the hours before sunset, but more recently, they have been distributed across the evening period. Based on template matching techniques, we have identified 16 distinct families that generally follow the temporal clusters. A thermal origin of these events is suggested, since the majority of the events fall within a ±2 h time window around sunset with extreme temperature changes. The SF events have similarities with thermal events observed on the lunar surface from data collected during the Apollo missions.
Plain Language Summary
The seismometers on Mars are recording high‐frequency signals of short duration. Seven hundred and eighty of these events have been found so far, that can be categorized into families with comparable signal shape. Each family repeats for a limited number of days at similar times of the day. At first, they occurred at or shortly before sunset, but more recently they are being observed later in the Martian evening. We infer these signals originate from close to the lander but not the lander itself, and may be related to thermal cracking, like the lunar thermal events observed during the Apollo missions.
Key Points
Super high frequency events are a class of signals observed by the InSight seismometer on Mars
Seven hundred and eighty events have been observed, typically lasting 20 s with energy mainly on horizontal components between 5 and 30 Hz
Events appear in clusters and are likely associated with local thermal sources similar to observations on the Moon
Clay slopes are susceptible to suddenly liquefy into rapidly accelerating landslides, thereby threatening people and facilities in mountainous areas. Because the shear-wave velocity (Vs) ...characterizes the medium stiffness, this parameter can potentially be used to investigate the rheological behavior of clay materials before and during the solid-to-fluid transition associated to such landslide failures. Previous rheometrical studies performed on clay samples coming from Trièves landslides (French Alps) have established that this material behaves as a yield stress fluid with a marked viscosity bifurcation. When the applied stress reaches a critical level, the viscosity decreases abruptly, along with Vs which tends to zero in the fully fluidized material. Here, we monitor the Rayleigh wave velocity (VR) variations in a saturated clay layer placed in a flume and progressively brought to failure by tilting the device. Experiments performed on clay samples with different water contents show a significant relative drop in VR values (and hence in Vs) before the onset of the mass movement. Additional rheometrical analyses point out that this precursory drop in Vs is presumably due to a complex transient rheological response of the clay. These new results confirm that Vs variations constitute a good indicator for monitoring clay slope stability.
•We model initiation of clay landslides in laboratory flume experiments.•We observe precursory drops in acoustic wave velocities prior to movement onset.•Rheometrical tests reveal a time-dependent rheological response of the clay.•Precursors and transient rheological response could be related.
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