Elsevier

Engineering Geology

Volume 279, 20 December 2020, 105860
Engineering Geology

Evolution assessment of structurally-controlled differential subsidence using SBAS and PS interferometry in an emblematic case in Central Mexico

https://doi.org/10.1016/j.enggeo.2020.105860Get rights and content

Highlights

  • Subsidence evolution is assessed using SBAS and PSI methodology complementarily.

  • Increasing, decreasing, and migration of subsidence were identified in the analysis.

  • Higher compressible sediment thickness correlates with high subsidence rates.

  • Groundwater extraction rates are linked with persistent and focused high subsidence.

  • Subsidence evolution assessment allow urban planning in hydrogeological hazard zones.

ABSTRACT

The city of Morelia has been affected by Structurally-Controlled Differential Subsidence (SCDS) since at least 1983, modifying civil structures and infrastructure through the appearance of ground failures and differential ground subsidence. The resulting damage to streets, homes, hydraulic lines, and government facilities has caused economic losses worth millions of dollars. An increase in population has led to the overexploitation of groundwater, which is the main trigger for SCDS, while the subsoil's geology and bedrock configuration are considered conditioning factors of this phenomenon. This paper offers an analysis of the SCDS evolution over the last fourteen years and its relationship with groundwater extraction and thickness of unconsolidated sediments. The former was carried out through SAR Interferometry techniques to detect and monitor land subsidence, using Small Baseline Subset (SBAS) from 2003 to 2010 and Persistent Scatterer Interferometry (PSI) from 2014 to 2017. Additionally, groundwater pumping well data and lithological information from boreholes enabled a spatial analysis to evaluate the role of these factors in the development and acceleration of SCDS. The SBAS results show maximum sinking rates of 2.2 cm/yr. with a spatial distribution that is clearly controlled by buried geological structures. In this period, the maximum sinking rates were induced by high groundwater extraction rates in focused areas, while intermediate rates were linked to notable depletion cones. The PSI results indicate a maximum sinking rate of 2.74 cm/yr. and an accelerated subsidence migration to the west, owing to the construction of new wells and persistent high groundwater extraction rates. For both periods, the larger compressible sediment package reveals a good correlation with high subsidence rates, mainly in the hanging wall blocks of the buried faults. The identification of differential subsidence accompanied by high sinking rates in novel areas of Morelia, as well as the detection of the subsidence migration, will provide scientific support to decision-makers for the proposal of engineering solutions and urban planning capable of reducing hydrogeological hazards associated with SCDS.

Introduction

Land subsidence is a geological phenomenon conditioned by the subsoil's geology (compressible sediment thickness, tectonic faults, or bedrock configuration) and triggered mainly by excessive groundwater extraction, often as a consequence of population explosion. Several cities around the world are affected by land subsidence, with some of the most relevant cases occurring in China (Zhu et al., 2020), Italy (Modoni et al., 2013), Spain (Bonì et al., 2015), USA (Galloway et al., 1999) and Mexico (Figueroa-Miranda et al., 2018). In Mexico, land subsidence has been classified into two main types: Mexico City Subsidence Type (MCST) and Structurally-Controlled Differential Subsidence (SCDS) (Figueroa-Miranda et al., 2018). SCDS is the most complex and widespread type, affecting thousands of people in over 40 cities in the tectonic valleys of Central Mexico. SCDS triggered by groundwater extraction is characterized through differential gradual sinking, discontinuities, and ground collapse aligned with the direction of a buried tectonic fault or bedrock configuration. The differential sinking occurs due to the contrast in sediment thickness on both sides of the tectonic fault trace. In the hanging wall block, the thickness of unconsolidated sediments is usually greater than in the foot wall block; this difference causes higher sinking in the former than in the latter (Fig.1b, c), thus producing the differential subsidence (Figueroa-Miranda et al., 2018). The SCDS in the urban area of Morelia was first recorded in 1983 as a series of fissures in walls of houses and buildings (Fig. 1) (Ávila-Olivera, 2004). The damage caused by differential subsidence and the appearance of discontinuities in the ground was mainly due to cracking and fissuring in civil structures causing millions in economic losses (Hernández-Madrigal et al., 2014). Since its identification in the city, the phenomenon has been studied and monitored with different measurement techniques (Table 1).

Among the ground and space-based geodetic methods used for monitoring land deformation, the differential InSAR technique (DInSAR) has proven to be a valuable tool for detecting and measuring the phenomenon on a large spatial scale, at a low cost, and with millimetric precision (Yerro et al., 2014). However, DInSAR has some limitations with atmospheric artifacts and a lack of image coherence due to spatio-temporal decorrelation. Moreover, this technique does not allow to determine the temporal behavior of detected ground deformations. Therefore, multi-temporal InSAR methods have emerged to overcome conventional DInSAR limitations. Over the last two decades, Small Baseline Subset (SBAS) (Casu et al., 2014) and Persistent Scatterer Interferometry (PSI) (Ferretti et al., 2001) have provided high spatial-resolution (up to 25 cm) for accurately (sub-centimeter to sub-millimeter accuracy) mapping the temporal and spatial distribution of ground deformation (Motagh et al., 2017; Nikos et al., 2016). Both techniques use point-like coherent targets, minimally affected by the decorrelation. These points are known as persistent scatterers (PS) and provide a time series of displacements for each scatterer over the entire analysis period. The SBAS technique reduces the decorrelation by exploiting distributed targets, thus it is widely used in undeveloped areas and large-scales (Yu et al., 2020). Furthermore, PSI enables a precise characterization of the linear deformation affecting urban areas (Foroughnia et al., 2019).

The objective of this work is to assess the evolution of long-term ground deformation in Morelia. For this purpose, two InSAR analysis (SBAS and PSI) were carried out over 14 years. These results were used in a complementary manner to evaluate changes in the intensity and migration of the subsidence, and its correlation with the conditioning (subsoil's geology) and triggering (groundwater extraction) factors. Assessing subsidence on a large temporal scale sometimes depends on the availability of SAR data and the platforms or software to process it. Therefore, SBAS processing was implemented on the G-POD (Grid Processing on Demand) platform, which is a web environment of the European Space Agency (De Luca and Casu, 2015). The stack included 28 SAR images from the ENVISAT satellite (descending orbit), dating from May 3, 2003 to September 18, 2010. The PSI processing was performed using the SNAP (Sentinel Application Platform) software (ESA, 2017) and the StaMPS/MTI (Stanford Method for Persistent Scatterers) algorithm (Hooper, 2009) applied to a stack of 29 Sentinel-1 images (descending-orbit) from October 25, 2014 to January 1, 2018. Furthermore, groundwater data from wells allowed to contrast the piezometric levels and extraction rates with the InSAR results. Finally, a deformable sediment thickness map derived from lithology boreholes defined the contribution of this variable to the SCDS spatial behavior.

Section snippets

Study area

The city of Morelia is a World Cultural Heritage Site located in the northeast portion of the state of Michoacán in Central Mexico (Fig. 2a). The urban area has an average elevation of 1920 m.a.s.l. and a population of 607,500 inhabitants (Population City, 2018). The climate in the city is predominantly sub-humid temperate (INEGI, 2016), and the average annual rainfall varies between 800 and 910 mm, 79% of which occurs from June to September (Figueroa-Miranda, 2019). The studied area has been

SBAS technique

SBAS processing was performed with 28 radar images obtained by the C-band ASAR sensor onboard the ENVISAT satellite. The scenes covered a period from May 3, 2003, to September 18, 2010. The images were acquired in S2 image mode (angle of view θ = 20.8°; fringe = 100 km) with VV polarization and along descending orbit (track 69, frame 3212). Processing was implemented in the G-POD (Grid Processing on Demand) environment which is a web environment of the ESA. This platform provides users with a

Analysis of SCDS through SBAS (2003−2010)

The G-POD platform identified 7235 PS within the study area, which represents an average density of 52.4 PS/km2. The average coherence of these PS is 0.92, which indicates high reliability in the deformation rates of the PS. As a result of the stability threshold, the remaining dataset included 3488 PS, indicating an average density of 25.2 PS/km2 (Fig. 4). The results of the SBAS analysis (2003–2010) indicate that Morelia shows a maximum deformation rate in LOS of 2.2 cm/yr. and a maximum

Discussion

InSAR techniques for detecting and monitoring land subsidence have been demonstrated to be very reliable at the global level (Motagh et al., 2017; Nikos et al., 2016). However, ground deformation values can vary according to several factors such as the satellite sensor, the InSAR technique, the processing methodology, or the temporality of the study. For this reason, the maximum deformation rates obtained previously for the city of Morelia are variable (Table 1); however, the spatial

Conclusions

In this paper, was evaluated Structurally-Controlled Differential Subsidence (SCDS) in the city of Morelia using two SAR interferometry techniques. In addition, was analyzed the role of groundwater and compressible sediment thickness as trigger-conditioning factors of the phenomenon. The InSAR SBAS technique was applied for a period of seven years (2003–2010) using ENVISAT images, while the PSI technique was developed for three years (2014–2017) with Sentinel-1 images. The data to evaluate the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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