DOI: 10.5066/p9ebijg5
title: Seismic data, point clouds, and rebound hammer data from the Trona Pinnacles, CA, in 2020 and 2021

description: Three complementary datasets are presented: seismic recordings; photogrammetric point clouds; and rebound hammer measurements. On 4-5 March 2020, U.S. Geological Survey simultaneously collected three-component seismic data from three sites within the Trona Pinnacles National Natural Landmark: the top of a "skinny" pinnacle; the top of a "stout" pinnacle; and at a "reference" site. The primary goal of the seismic survey was to characterize the seismic response of the pinnacles, which are naturally occurring towers composed of tufa rock. Many pinnacles exhibit low height-to-width ratios; these are termed "stout". Pinnacles with higher height-to-width ratios, greater than approximately 2.0, are termed "skinny". The reference site is flat tufa exposure at the ground surface, located within approximately 1 kilometer of the other sites. At each site, a Trillium Compact broadband sensor was levelled, oriented to true north, and attached to intact tufa with plaster. The sensors were then covered with weighted buckets. Reftek RT-130 or RT-130s dataloggers were used to record data overnight. Global positioning system antennae provided accurate timing. The datalogger at the reference site malfunctioned after several hours, but at least two aftershocks of the 2019 Ridgecrest earthquake sequence were recorded at all three sites. The largest aftershock was a M1.9 located within 20 km. Here, we provide the raw data in miniseed format (https://ds.iris.edu/ds/nodes/dmc/data/formats/miniseed/) and the instrument parameters necessary to calculate ground motion (https://www.passcal.nmt.edu/content/instrumentation/field-procedures/working-responses-get-units-displacement). The filenames consist of 13 digits that describe the decimal time the file was written, followed by four characters describing the datalogger name, followed by two digits describing the sensor channel. Also in 2020, 3-dimensional point clouds were produced for the Stout and Skinny pinnacles using photogrammetric methods. These digital models of the pinnacles provide the basis for future studies to model their seismic responses. Finally, in 2021, U.S. Geological Survey also attempted to collect rebound hammer data at the sixteen of the Trona Pinnacles. The goal of the rebound hammer survey was to characterize hardness contrasts in the tufa rock, which are potentially consistent with damage accumulation. Rock damage may occur during shaking due to earthquakes or ambient noise in the environment. The pinnacles were selected for measurements because they exhibited a representative range of height-to-width ratios. The pinnacles are typically 3-10 meters in height. At each of these pinnacles, two groups of rebound hammer measurements were made on approximately orthogonal faces, for a total of four groups per pinnacle. At each rock face, one group of measurements was made as close to the rock-soil interface as practical, usually within 1 meter of the ground. Another group was made at least 2 meters higher than than the first group. This sampling strategy was designed to identify potential differences in hardness between the bases of the pinnacles and the midsections. Each group consists of ten measurements that were made using a slightly modified version of the standard test method for determination of rock hardness by rebound hammer method (American Society for Testing and Materials Standard 04.09 (D 5873-00)). The single deviation from this method was that no effort was made to polish the tufa rock surface prior to measurement. Tufa is porous rock, and polishing was not a reliable method for achieving a flat, clean rock face for contact with the rebound hammer. Instead of polishing, extreme care was taken to identify areas of the rock face where the existing tufa was clean and smooth. Care was also taken to ensure that the tufa rock facies was identical for the base and midsection groups. Unfortunately, these considerations precluded the possibility of making measurements on similarly oriented faces on all pinnacles. The orientations of the measured rock faces varied widely from pinnacle to pinnacle. Here, we provide the results from a Schmidt L-type rebound hammer, corrected to horizontal measurement angle, per ASTM D5873. Measurements are provided for only fourteen of sixteen pinnacles. Poor rock quality at two pinnacles precluded meaningful rebound hammer measurements; at these two, the rock consistently showed permanent plastic deformation when struck by the hammer.