Simon Christian Stähler

Last Name

Stähler

First Name

Simon Christian

ORCID

0000-0002-0783-2489

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09815 - Zurbuchen, Thomas H. / Zurbuchen, Thomas H.

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Publications 1 - 10 of 144

Applications of Time-Frequency Domain Polarization Filtering to InSight Seismic Data
Brinkman, Nienke; Sollberger, David Andres; Schmelzbach, Cédric; et al. (2023)
Earth and Space Science
The seismometer Seismic Experiment for Interior Structure (SEIS) onboard the InSight lander was used to continuously record the seismicity on Mars from February 2019 to December 2022. To maximize the information that can be extracted from the seismic data, it is critical to identify and to suppress undesired features (e.g., environmental noise, scattered waves, seismic imprint of lander vibrations) and non-seismic noise (e.g., instrument related artifacts). We present an advanced polarization filtering workflow in the time-frequency domain to suppress undesired features and to enhance the signal-to-noise ratio of the SEIS recordings. We estimate time-frequency-dependent polarization attributes such as the ellipticity, directionality of the particle motion, and the degree of polarization to identify and filter out undesired data parts. After filtering in the time-frequency domain, the seismic data are transformed back to the time domain, yielding broadband waveform data that can be used for further seismological analysis. We illustrate the benefits of our filtering approach with three use cases. Firstly, we show how polarization filtered data can help to constrain the source mechanism of the sol 1,222 event, the largest marsquake detected so far. Using the proposed polarization filtering techniques, we are able to enhance the S-wave arrival by suppressing interfering randomly polarized scattered waves to successfully infer on the moment tensor of this event. Secondly, we show that polarization filters can be used to suppress instrument-related glitches and, thirdly, to remove the seismic imprint left by the vibrating lander (mechanical resonances of the lander).
High‐Frequency Seismic Events on Mars Observed by InSight
van Driel, Martin; Ceylan, Savas; Clinton, John Francis; et al. (2021)
Journal of Geophysical Research: Planets
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. © 2021 American Geophysical Union
Performance report of the RHUM-RUM ocean bottom seismometer network around La Réunion, western Indian Ocean
Stähler, Simon Christian; Sigloch, Karin; Hosseini, Kasra; et al. (2016)
Advances in Geosciences
RHUM-RUM is a German-French seismological experiment based on the sea floor surrounding the island of La Réunion, western Indian Ocean (Barruol and Sigloch, 2013). Its primary objective is to clarify the presence or absence of a mantle plume beneath the Reunion volcanic hotspot. RHUM-RUM's central component is a 13-month deployment (October 2012 to November 2013) of 57 broadband ocean bottom seismometers (OBS) and hydrophones over an area of 2000  ×  2000 km2 surrounding the hotspot. The array contained 48 wideband OBS from the German DEPAS pool and 9 broadband OBS from the French INSU pool. It is the largest deployment of DEPAS and INSU OBS so far, and the first joint experiment. This article reviews network performance and data quality: of the 57 stations, 46 and 53 yielded good seismometer and hydrophone recordings, respectively. The 19 751 total deployment days yielded 18 735 days of hydrophone recordings and 15 941 days of seismometer recordings, which are 94 and 80 % of the theoretically possible yields. The INSU seismic sensors stand away from their OBS frames, whereas the DEPAS sensors are integrated into their frames. At long periods (>  10 s), the DEPAS seismometers are affected by significantly stronger noise than the INSU seismometers. On the horizontal components, this can be explained by tilting of the frame and buoy assemblage, e.g. through the action of ocean-bottom currents, but in addition the DEPAS intruments are affected by significant self-noise at long periods, including on the vertical channels. By comparison, the INSU instruments are much quieter at periods >  30 s and hence better suited for long-period signals studies. The trade-off of the instrument design is that the integrated DEPAS setup is easier to deploy and recover, especially when large numbers of stations are involved. Additionally, the wideband sensor has only half the power consumption of the broadband INSU seismometers. For the first time, this article publishes response information of the DEPAS instruments, which is necessary for any project where true ground displacement is of interest. The data will become publicly available at the end of 2017.
Enhancement of Seismic Phase Identification using Polarization Filtering and Array Analysis
Ling, Angel; Stähler, Simon Christian; Sollberger, David Andres; et al. (2023)
EGUsphere
Single-station polarization analysis allows us to extract wave parameters, such as inclination, azimuth, and ellipticity angle, directly from a recorded seismic signal theoretically. In reality, however, seismic data are not purely polarized in the finite analysis window due to varying noise levels, complex wavefield interactions, and calibration errors. Hence, this would potentially influence the observation window of phases of interest. In order to minimize these systematic errors, the involvement of arrays and array processing techniques can further increase the signal-to-noise ratio of coherent signals in a wavefield, which allows us to identify different seismic phases, especially the weaker phases that are usually difficult to observe in a single waveform, even after filtering for a desired wave type. In this study, we present a new approach that combines polarization analysis and filtering in the time-frequency domain using the S-transform with conventional array analysis such as beamforming to enhance seismic signals and distinguish different phases based on their expected slownesses and backazimuth. We apply this approach on AlpArray data and demonstrate wavefield separation in vespagrams using various polarization filters. We also discuss the benefits of our approach especially on small amplitude inner core phases (e.g., PKIKPPKIKP) and their applications for advancing seismological study of Earth’s inner core.
Surface waves and crustal structure on Mars
Kim, Doyeon; Banerdt, William Bruce; Ceylan, Savas; et al. (2022)
Science
We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.
Lunarleaper - Unlocking a Subsurface World
Mittelholz, Anna; Stähler, Simon Christian; Kolvenbach, Hendrik; et al. (2024)
EGUsphere
We present LunarLeaper, a robotic explorer concept in response to the ESA 2023 Small Missions call. Pits, volcanic collapse features with near-vertical walls, have been identified across the lunar and Martian surface. These pits are high priority exploration destinations because some, referred to as skylights, might provide access to subsurface lava tube systems. Lava tubes are of particular interest for future human exploration as they offer protection from harmful radiation, micrometeorites and provide temperate and more stable thermal environments compared to the lunar surface. We propose to use a small legged robot (ETH SpaceHopper, <10 kg), to access and investigate the pit edge, using its ability to access complex and steep terrain more safely than a wheeled rover. LunarLeaper will land in Marius Hills within a few 100 m of the pit and traverse across the lateral extent of the hypothesized subsurface lava tube. On its traverse it will take measurements with a ground penetrating radar and a gravimeter, measurements that will allow us to survey the subsurface structure and detect and map lava tube geometry if present. The robot will approach the pit edges and acquire high resolution images of the pit walls containing uniquely exposed layers of the geophysically mapped lava flows and regolith layers. These images will allow not only scientific advances of lunar volcanism and regolith formation, but also enable assessment of the stability of the pit structure and its use as a possible lunar base. The mission is expected to last 1 lunar day. The robot could be delivered to the surface by a small lander, as they are currently developed and planned by various national and commercial agencies and hop off the landing platform without the need for a robotic arm. It is highly flexible in accommodation and can thus make full use of the new international lunar ecosystem.
First observations of core-transiting seismic phases on Mars
Irving, Jessica C.E.; Lekić, Vedran; Durán, Cecilia; et al. (2023)
Proceedings of the National Academy of Sciences of the United States of America
We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars' core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars' core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core-mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars' core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution.
Seasonal seismic activity on Mars
Knapmeyer, Martin; Stähler, Simon Christian; Daubar, Ingrid J.; et al. (2021)
Earth and Planetary Science Letters
The rate of occurrence of High Frequency (HF) marsquakes, as recorded by InSight at Homestead Hollow, Elysium Planitia, increased after about Ls =33°, and ceased almost completely by Ls =187°, following an apparently seasonal variation with a peak rate near aphelion. We define seismic rate models based on the declination of the Sun, annual solar tides, and the annual CO2 cycle as measured by atmospheric pressure. Evaluation of Akaike weights and evidence ratios shows that the declination of the Sun is the most likely, and the CO2 cycle the least likely driver of this seismic activity, although the discrimination is weak, and the occurrence of a few events in August 2020 is in favor for a triggering by CO2 ice load. We also show that no periodicity related to Phobos' orbit is present in the HF event sequence. Event rate forecasts are presented to allow further discrimination of candidate mechanisms from future observations.
Clock errors in land and ocean bottom seismograms: high-accuracy estimates from multiple-component noise cross-correlations
Hable, Sarah; Sigloch, Karin; Barruol, Guilhem; et al. (2018)
Geophysical Journal International
Geophysical Observations of Phobos Transits by InSight
Stähler, Simon Christian; Widmer-Schnidrig, Rudolf; Scholz, John-Robert; et al. (2020)
Geophysical Research Letters
Since landing on Mars, the NASA InSight lander has witnessed eight Phobos and one Deimos transits. All transits could be observed by a drop in the solar array current and the surface temperature, but more surprisingly, for several ones, a clear signature was recorded with the seismic sensors and the magnetometer. We present a preliminary interpretation of the seismometer data as temperature‐induced local deformation of the ground, supported by terrestrial analog experiments and finite‐element modeling. The magnetic signature is most likely induced by changing currents from the solar arrays. While the observations are not fully understood yet, the recording of transit‐related phenomena with high sampling rate will allow more precise measurements of the transit times, thus providing additional constraints for the orbital parameters of Phobos. The response of the seismometer can potentially also be used to constrain the thermoelastic properties of the shallow regolith at the landing site. © 2020 American Geophysical Union

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Simon Christian Stähler

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